Wikipedia:Reference desk/Archives/Computing/2010 January 26

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January 26

TOR inside a LAN and destination IPs

If I use TOR inside a LAN, can the LAN admins see which websites I'm visiting based on the network traffic? 218.25.32.210 (talk) 00:37, 26 January 2010 (UTC)

Ideally, all they see is the IPs of the Tor nodes that you communicate with (which doesn't tell them much). But you don't set things up correctly, they can see the DNS lookups you do (see Tor (anonymity network)#DNS leaks) which of course can itself be very enlightening. In addition, the operators of the exit nodes, where your traffic leaves the TOR network, can see everything you're doing (and as you don't know who they are, why should you trust them). See Onion routing#Weaknesses. Oh, and are you sure that the Tor client you're using is really the real Tor client, or a hacked one that the LAN admins have substituted instead? If you're concerned enough to use Tor, you should be concerned enough to worry about that kind of thing. -- Finlay McWalter • Talk 00:56, 26 January 2010 (UTC)

Adding to the above, if the machines are installed/managed by people other than yourself then it'd be safer to error on the side of caution and say "yes they can". It's completely possible they might have monitoring software installed which might log keystrokes or addresses typed into the browser or anything at all really. They could even have something like VNC installed and simply just "watch" your screen without you even knowing ZX81 ^talk 01:09, 26 January 2010 (UTC)

And note this. -- Finlay McWalter • Talk 01:13, 26 January 2010 (UTC)

Also (as the linked articles above say) Tor has very limited resistance to traffic analysis and timing analysis attacks. Some kinds of traffic have very distinctive patterns, which you can discern even when the content of packets is encrypted and their IP addresses intermediated. p2p traffic does lots of traffic, is roughly symmetrical (about as much is sent as is received), and opens lots of sockets. Email tends to be periodic, and if you get as much spam as me then you download much more than you upload. The same is true for online video like Youtube, but that consists of lengthy runs of downloads with negligible upload. So if your intention is, for example, to do p2p on a network that forbids it, Tor will only be of some use. -- Finlay McWalter • Talk 01:13, 26 January 2010 (UTC)

Well, I'd be running Tor on my own hardware (laptop) hooked into their LAN. The copy of Tor I have is legit, coming directly from the Tor Project. So that excludes keyloggers and screen monitors. Everyone uses the internet here, so I figured the traffic would look just like any other user's except that the IPs would be other computers, not websites, right? 218.25.32.210 (talk) 01:18, 26 January 2010 (UTC)

How to you know it came from the Tor Project website? Did you check the binary checksums, and did you verify those checksums were the same when viewing the site from several unrelated networks? Detecting Tor traffic is trivial: firstly it's all encrypted (something almost all traffic done by non-tor users isn't), and secondly (as most Tor nodes are run from someone's home cable or adsl connection) most of your traffic will be going to random addresses in BT and Pacbell and Telstra address blocks, and not to the big providers like Google and MSN and BBC. I know to an absolute certitude that my own ISP notices connections from my adsl connection to other home-or-small-office connections (they're looking for zombies phoning home) so evidently existing network monitoring systems already check for that. -- Finlay McWalter • Talk 01:28, 26 January 2010 (UTC)

Thanks for the persistent explanations, Finlay! 218.25.32.210 (talk) 02:01, 26 January 2010 (UTC)

You're welcome. In practice whether Tor is sufficient for your purposes depends on what your purposes are. If you just want to edit your secret Facebook account, or download the odd video from veryhairychicksallegedlynaked.com then Tor is sufficient. If you want to plot revolt against an autocratic government, probably not. -- Finlay McWalter • Talk 02:26, 26 January 2010 (UTC)

Just want to point out that be careful what you check. Checksums are strictly speaking only intended to guard against accidental modification (such as download error). For checksums like CRC32 for example, it is trivial to generate a file which gives the same checksum with different content. While things like SHA256 are commonly called checksums (and it's arguably an accurate name), the key point is that they are cryptographic hash functions (i.e. secure hashes) and are intended to guard against malicious modification. Generally speaking, if authenticity verification is intended against malicious modification, cyptographic hashes will be provided and perhaps they won't even provide checks that are not secure hashes (like CRC32), it is important you make sure you do check against a secure hash if you are concerned with such things. Also consider the source of the hash. If for example your using the same network which you don't trust and don't have a secure connection to the server then it's pointless trusting the hash Nil Einne (talk) 12:22, 28 January 2010 (UTC)

wants to get data structures subjects

I want full information about data structures —Preceding unsigned comment added by 115.118.113.50 (talk) 06:32, 26 January 2010 (UTC)

Whole university courses are given on this topic, so you are unlikely to get full information in a reply here. Our article on Data Structure won't be of much help for the detail, except that it might have some useful links. There is a Wiki Book on Data Structures[1] that gives an outline of each structure. You will need to read several text books if you want to study the subject in detail. Dbfirs 10:24, 26 January 2010 (UTC)

The differences beetween white DVD and purple DVD

There are 2 types of CD. The most popular is "green" CDs, whose bottom's color is green (not exactly green), which we usually use to burn data to. The other one is "white" CDs, whose bottom's color is white, which we may obtain from offical software publisher. The white CDs often are the original CDs, and the blue one are always pirate. There is the same thing with purple DVDs and white DVDs.

Some wise one plz explain the difference of these to me. All I know is that the white CD/DVD lasts longer than the other, and that it can be play even if it is quite rough, but the green/purple won't. What are exactly purple DVD and white DVD? Why do they have different colors? Why does the white one last longer? The time it lasts also depend on burning speed, is that true?

Besides, I hear that all white DVDs work well on PlayStation 2, but the purple DVDs don't -- it depends on purple DVD type, some work, some not. Is that true? And, they also say that to get a DVD work on PS2, I must burn it at the slowest speed possible (ie: 2x). I always burn CDs with 52x speed and it work well on PC but high speed burning shall make the disc cannot be play on PS2, why? The console has so much... troubles. -- Livy the pixie (talk) 09:06, 26 January 2010 (UTC)

I've never heard the white, green and purple terms, but anyway ... CDs (and DVDs) that are produced by the publisher are generally stamped, not burned. Areas called "pits" and "lands" which are roughly analogous to the 0s and 1s that make up all binary data are stamped into the molten plastic, which is then coated with metal. See the Manufacturing section of Compact Disc and the more detailed article linked from there. Discs which can be or have been burned contain layers of dyes which change reflectivity during the burning process; these areas of differing relectivity can be interpreted the same way pits and lands can be. See the Recordable CD portion of Compact Disc or CD-R. One reason that your "white" discs last longer is that the dyes used in recordable discs may deteriorate. See Disc rot.

I can not comment on the PS2 considerations, I'll leave that to somebody more familiar with gaming consoles.

Finally, though, I wanted to point out that CD-Rs (at least) are available in many colors - here is one example. It's not completely clear from the product image on that page, but the five colors they show are on the recordable side of the disc (as well as the top, if I recall correctly) --LarryMac | Talk 13:34, 26 January 2010 (UTC)

Stamp? I've never heard of this term before -- I'm a noob indeed. In my country, holding a disc in hand, we always say that all data (in the disc) is already "printed" to it as if it is a paper. It is a habit since it is easy to understand. If you say "burn a CD", then they will think of setting fire to a CD to burn it into ash, lol. The term "burn" is used rarely by teenagers only. We use it in original English, not translated, and it means "write data to disc", no matter that disc is stamped or burned, so that I really don't know what is "stamp". I have no knowledge 'bout such aspect. Stamping and burning are two different methods of writing data into a disc? Can you explain further? If true, then the green/purple discs I mention above must be burned discs and the white ones must be stamped discs. -- Livy the pixie (talk) 14:11, 26 January 2010 (UTC)

See our articles on Compact Disc manufacturing, Compact Disc, CD-R and CD-RW. Gandalf61 (talk) 16:07, 26 January 2010 (UTC)

• Stamping and burning are in the end different ways of putting data onto a disc. In 'stamping' the data is put on during manufacture of the disc, in 'burning' the disc is made first, then the data is put on the disc by the laser in a CD/DVD drive. The end result is much the same, a disc that can have data read from it. Stamping means to press one thing onto another with force, such as raising your foot and stamping your heel on the ground.
• I think when you say 'white' you actually mean silver, which is the colour of mass produced stamped optical discs due to the layer of silver an alloy of (mostly) aluminium that is put on them during manufacture. This will deteriorate far less than the dyes in recordable discs so should last much longer. --220.101.28.25 (talk) 16:19, 26 January 2010 (UTC)

My thanks. Now that I got it. The alloy of aluminium makes the silver color of stamped discs, which burned discs do not have. But what about the burning speed problem with PlayStation 2? Many say that if a PS2 DVD is burned at above 4x speed, it is hardly to run properly. The loading time of the game is awful long, and the disc even does not run. It sounds odd, but they claimed that they had tested themselves -- many said that. I kinda doubt it. How does burning speed affect the disc? -- Livy the pixie (talk) 17:05, 26 January 2010 (UTC)

Sorry Livy, I too don't know much about the PS2 side of things, theoretically, as you are talking about game discs, then I expect this is a deliberate move by Sony to help protect the copyright of the game manufacturers. That is they make it hard to make good copies by a copy protection scheme. Going back to stamped vs. burned discs, I recommend that you read through the Compact Disc manufacturing article and other articles as suggested by LarryMac and Gandalf, as I got a few things wrong before I checked it there. ie. I believed that silver was used to coat the discs. --220.101.28.25 (talk) 17:58, 26 January 2010 (UTC)

"articles as suggested by Gandalf"... harrumph! --LarryMac | Talk 20:26, 26 January 2010 (UTC)

Apologies, corrected 220.101.28.25 (talk) 12:07, 27 January 2010 (UTC)

Whether you burn a DVD at 1x, 2x, or 4x should make no difference if you have a properly working DVD writer. Actually, when recordable CDs were new, Sony's big external SCSI 2x CD burner came with instructions saying that you were supposed to burn CDs at 2x and not 1x, because at 1x there was increased disc wobble, and the number of uncorrectable errors burned to disc was expected to be higher. Based on that, I would speculate that burning at low speeds probably does not help. Anyway, you are asking for advice about a PlayStation 2 that has obviously been "chipped" or "modded" so it can play pirated games — you don't say where you're from, but in some countries, I understand, all available PS2s are chipped — so I would expect unreliability would be due to the chipped PS2, rather than being due to the pirated game discs you are trying to play. It could be that the PS2 copy protection system is actually functioning here. Comet Tuttle (talk) 19:35, 26 January 2010 (UTC)

Comet Tuttle has a point, although some suggest to burn CDs and DVDs at the lowest possible speed, this is often poor advice. In fact this is usually a bad idea with modern burners and media. Very commonly they will perform very poorly when burning at the lowest speed. I'm not saying to burn at the highest possible speed. With CD & DVDs, we've started to reach the level where sometimes burning at the highest speed can generate poor burns, even worse if you have shitty media to begin with (which makes up most of the media). However I wouldn't recommend 4x. 8x or 12x perhaps. Certain drives enable you to do error checking on the CD/DVD with the right software. E.g. Nero CD/DVD speed. These can give you an idea of the PI/PO errors of your burn on that drive (basically how many errors the drive gets on reading that it auto corrects). You may want to check out MyCE formerly known as CDfreaks for more info on how burn quality can vary with speed and other factors. Nil Einne (talk) 06:13, 27 January 2010 (UTC)

There are actually 3 different dyes that are used with CDR which give different colours. These dyes may also sometimes be mixed. And the precise colour you see will depend on whether silver or gold or gold & silver are used for the reflective coat. And according to our article, some manufacturers may colour the dye anyway. These provides more info [2] [3] CD-R. The colour of the top side can of course be whatever you want since you can just print on it. DVD dyes also vary, but this doesn't affect the colour you see much Nil Einne (talk) 06:25, 27 January 2010 (UTC)

Execute a file when computer has been inactive.

Is there any way to set your computer to execute a file when it has been inactive for certain number of minutes?  Hamza  ^{[ talk ]} 09:22, 26 January 2010 (UTC)

It would be trivial to write a Windows application that restarts a timer at each key or mouse event, and then ShellExecutes something when the timer has reached a certain value. But perhaps you can use Windows task scheduler for this - I do not know. --Andreas Rejbrand (talk) 11:25, 26 January 2010 (UTC)

Well, I work for the USAF, and computers here are programmed to do pretty much exactly that. If there has been no activity for five minutes, they automatically self-lock. I've wondered about the possibility of [someone, not me... I'm not a programmer] writing an "idle timer," so to speak, so one could see how close they're getting to the five minutes. I'll Google it, but does anyone already know of one? Kingsfold (talk) 13:20, 27 January 2010 (UTC)

I now checked, and you can use Windows Task Scheduler for this. Simply create a new task and select "Inactivity" as the triggering event. --Andreas Rejbrand (talk) 11:30, 26 January 2010 (UTC)

I can't see that option in Windows XP. Actually a program that executes after a certain amount of inactivity is usually called a Screensaver - maybe you can cheat by renaming the exe file with an extension of .scr and setting that as your screensaver (in Control Panel/Display/Screen Saver). AndrewWTaylor (talk) 12:21, 26 January 2010 (UTC)

I've already checked Task Scheduler in XP. As Andrew said, there is not inactivity option in it. Is there any freeware that can do it?  Hamza  ^{[ talk ]} 15:49, 26 January 2010 (UTC)

I just created a scheduled task in Windows XP and found a relevant "When idle" option. It's not shown in the "Add Scheduled Task" wizard, but is available if you look in the properties window of the task. --Bavi H (talk) 02:14, 27 January 2010 (UTC)

Why am I spam?

I send emails to myself so I can be on any computer when I send them or when I receive them. I could store documents on my own computer but I never have, since I didn't have one for so long.

But this is a new problem. I used my Yahoo address to send an email to myself, and the email containing the information I wanted to send was in the sent folder. This meant when I replied to it with additional information, I replied to the same address. Believe it or not, this ended up in the spam folder!Vchimpanzee · talk · contributions · 14:17, 26 January 2010 (UTC)

Many modern anti-spam techniques use heuristic techniques like Bayesian spam filtering, which weigh a number of factors when assessing each candidate email. Some anti-spam systems (such as Spam assassin) add email headers to emails as they process them, which explain the statistical reasoning used for assessing a given email (so get your email client to show you the headers for the emails in question). Common reasons are magic words like viagra (I guess this isn't the case for you), HTML emails, mostly or entirely binary (that is radix encoded) emails (which does sound like what you're doing), forged (or forged-looking) sender or from fields (if you're sending to yourself or an account that looks almost like yours, that might trigger it), lots of non-ascii characters (particularly an odd mixture of characters found in different alphabets, in a manner that you wouldn't find in real human writing in any language). Any decent anti-spam system should have a mechanism to whitelist a given sender, so you should be able to avoid this happening again. -- Finlay McWalter • Talk 14:31, 26 January 2010 (UTC)

In other words, you triggered a false positive on the default spam settings. You may have to change the filter from the default settings, (adding yourself to a whitelist is the easiest way to do this, as Finlay suggested). This Yahoo Help page, and others linked from it, may help. Nimur (talk) 14:50, 26 January 2010 (UTC)

That's right. By the way, if you're wondering why Yahoo hasn't configured their e-mail system to automatically place "e-mails from me" in the Inbox and never in the spam folder: It's because many people (including me) get a lot of spam that forges the "from" address to look like it's from themselves. It's a common attempt to get you to read the spam. Unfortunately this also means that when you whitelist yourself as suggested above, you may get a little more spam in your inbox that appears to be from you. One last recommendation: I know you have said in the past that you prefer to stick with the familiar, but Google Docs is a way better way to work on documents from multiple computers, compared to eternally e-mailing stuff to yourself. You just sign in with your Google account name from wherever you are and work on the documents. Comet Tuttle (talk) 17:26, 26 January 2010 (UTC)

surfing sux

ok, I have IE8 and windows basic vista and a slow (uk typical) internet connection of 1/2 mb.

I think this is now equivalent to surfing with an old style modem.

Here is an example, I go to bbc news.....lag of 7 seconds.Then I go to facebook ...freeze....shoutdown browser. restart go to another forum... lag... then it all works perfect for 1/2 hr. I make a cup of tea and come back ... lag,freeze,shutdown restart ... wireless signal lost.

Then it all works the next day.,,,,, then.... the cycle of bullshit is repeated.

my questions are:

1) Has the net slowed down in general? 2) Are stupid flash designers the cause... overdoing there web design? 3) No Im not switching OS so what can i do about it!!!

Whoa — wireless signal lost? I think that's the problem. If you want to verify that this is the problem, hook up your computer with an Ethernet cable to your router for a few minutes and try surfing; wired connections are fast and reliable. If you find your Web surfing to be 100 times better, then we've narrowed down the problem to wireless connectivity. Comet Tuttle (talk) 17:33, 26 January 2010 (UTC)

(edit conflict) From what you've said about "wireless signal lost" it suggests to me that the problems are not necessarily to do with your Internet connection, but rather your connection to your wireless access point/router. What signal strength does it show you as having? If you have an low/poor connection then it would drop out frequently and you would experience pauses like you have described. Is it possible to position yourself closer to the access point (even temporarily) and see if you have the same problems? ZX81 ^talk 17:34, 26 January 2010 (UTC)

Adding to the above, the freeze on Facebook is likely caused by the wireless going down. Facebook uses AJAX to enable a lot of its functionality, and if the internet connection is lost, the code that pulls updates from the site may go hinky, possibly looping infinitely trying to acquire the data and crippling the page responsiveness. Of course, using IE8, each tab is a process, so a freeze in one shouldn't affect the others, but if your wireless has gone down, that won't do you much good. —ShadowRanger ^(talk|stalk) 17:59, 26 January 2010 (UTC)

Actually IE8 isn't guaranteed to use a seperate process for each tab. I was under the impression they use up to 3 processes total for tabs because according to Microsoft their research suggests most people don't use more then 3 tabs however it seems I was wrong. They may use more but it depends on your computer. Look at both the blog entry and the comment from Andy here. Note also that if one process/tab is using very high CPU (and you have a single core CPU or it's multithreaded) or very high RAM, you could get slowdowns for the whole computer including every other process. I have had this before due to unknown bugs (probably Flash or Java) Nil Einne (talk) 08:24, 27 January 2010 (UTC)

What sort of environment are you in? How far away from your wireless router are you? 10m is about the maximum indoors. Are there any obstacles in between your laptop and wireless router? What are they made of; thin plasterboard, or bricks, mortar and bits of metal? Are there any sources of interference? If you can pick up lots of other people's wireless networks, they may be causing you interference, but other devices like cordless landline (not mobiles - they use different frequencies) phones and microwave ovens - anything in the 2.4GHz ISM band - can also cause interference. CaptainVindaloo ^{t c e} 11:56, 27 January 2010 (UTC)

File permissions?

I opened one of my documents and made a quick change, then tried to close and save it. However, Word informed me that "Word cannot complete the save due to a file permission error," including in parentheses the location on my hard drive. I haven't done any meta-file mumbo jumbo with the document since I last edited it (last night), so what could have happened? How should I solve it? I already tried to check out the permissions for the file, but nothing seemed out of the ordinary. I was able to edit a document in the same folder as it...--The Ninth Bright Shiner 22:29, 26 January 2010 (UTC)

File / Save As seems to be the way out of the immediate problem; and if not, then a cut and paste of the content into a new file. Do you by chance make use of Live OneCare? Long discussion here, seems to be anti-virus products and/or an acer driver not getting on with an MS product. --Tagishsimon (talk) 22:44, 26 January 2010 (UTC)

Adobe/Acrobat product suite questions

Our office computers have Adobe Standard 6.0 installed on them -- more than the Reader, but less than the full Acrobat Professional suite. With this version, I can not only view PDFs, but also highlight, make minor text changes, and I have "Adobe PDF" as a system printer, which allows me to create PDF files from anything that can print. (This was once known as the Distiller; it may have a different name today.)

Q1: When I use those additional features, am I using the same executable of Reader as I might have downloaded, but with permissions to do the other stuff, or am I using a completely different executable to do the other features? It appears to be acroread.exe, but I'm not sure if that's the whole story. (Maybe there are different DLLs that enable the other features?)

Obviously, V6 is two releases out of date. I really should upgrade one of these days. The answer to Q1 probably impacts the answers to the rest of these:

Q2: If I download/install just the V7 reader, and I use the PDF printer, will I generate V6 or V7 PDF files?

Q3: If I download/install just the V7 reader, will I lose my capability for highlighting and markups? Or, in order to maintain those features, do I have to download something more than just the reader?

Q3a: If I have to install "something more", do I have to pay for the whole enchilada again, or is that considered a free upgrade?

Many thanks to those who have trod this path before. DaHorsesMouth (talk) 23:41, 26 January 2010 (UTC)

A1: It's a completely different executable. You can have both Acrobat and Reader installed on the same machine and they will operate independently of each other, however whichever one was installed last (probably Reader) will try and take over the default "pdf" file association (which you can swap back) as well as be the reader in your browser (which you probably want anyway) (and you're actually 3 versions behind as V9 is out now)

A2: The PDF printer won't be upgraded and will still create exactly the same same V6 files it did before.

A3: No, you can still open Acrobat as before and do editing as you did before, but watch out for the file associations as mention in A1.

On my work computer I have Acrobat 8 Standard and Reader 9, they work just fine together, but I had to change the PDF associations back to V8 ZX81 ^talk 01:03, 27 January 2010 (UTC)

OK, I think I get it. Any advice on whether upgrading Standard is fee or free? Thanks!
Wow, I could have had a V8? DaHorsesMouth (talk) 03:27, 27 January 2010 (UTC)

Sorry, but all upgrades of Acrobat to a newer version require payment. They offer free updates within the same version number (i.e. 8.0 -> 8.2) but anything else is considered a new product. They do offer cheaper upgrade pricing though for existing customers. ZX81 ^talk 03:52, 27 January 2010 (UTC)

Just keep in mind that Adobe Acrobat and Adobe Reader are two entirely difference software suites. Standard costs money in all of its form, Reader is free. So if you upgrade Standard to a new version, that will require money. Upgrading Reader costs nothing. --98.217.71.237 (talk) 13:47, 27 January 2010 (UTC)