Are there any legitimate uses for peer-to-peer file sharing programs?

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Hi Leo -- What security risks do P2P downloads have? How do you know that one of the peers has not corrupted the file?

Every file has a hash. If the file doesn't match that of the original file everyone else is sharing (which is the same copy as the first, original upload), it will not be shared. In fact, the torrent will warn you that a file does not match and wont share it to other peers.

As far as corruption while downloading.. It wont happen. The Transport Layer of the TCP/IP model insures that. If a packet is received corrupted, it will simply request the packet again and wait for it. TCP/IP insures that:
* data arrives in-order
* data has minimal error (i.e. correctness)
* duplicate data is discarded
* lost/discarded packets are resent

All of that still doesn't mean that you can't download a dangerous file. Many times a file is labeled with the name of a desired file only to contain a Trojan or worse.

After downloading your file AND BEFORE OPENING IT, let your antivirus program take a look at it. This one extra step has saved my own @ss many times.

Interesting quick tip with bittorrent that I noticed that other day:

If you are trying to download a torrent, and it suddenly becomes unavailable (and the download process turns "red" on the screen) then you can "repair your Internet" connection.

To do this you right-click the Internet connection icon on the bottom right of your screen, in the "system-tray" (with XP).

You then select the option "Repair Connection".

By repairing the connection it seems to force your computer to find new peers, and some of those new peers may then hold the parts of the file that you need.

This technique works quite well for me.

Also... whenever I use bittorrent, I find that my Internet slows to a snail pace.

This is probably because my computer is using the limited band width of my Internet connection to send out parts of multiple files, and make connections with many other bittorrent users (peers).

If you want to see just how many peers you are connected to, you can use a couple of easy commands.

When you reboot your computer, press Windows-R key to bring up the run prompt. Type "cmd".

Once you are in the command line, type:
netstat -b

That will show you all the connections you have to the "outside world".

Next, run your bittorrent program, and wait a few minutes. Then type that command again:
netstat -b

You will see yourself suddenly connected to people all around the planet -- sometimes hundreds of them. The list can grow to be really long.

If you want to disconnect all those people to speed up your internet again, once you are finished with Bittorrent, you can type these 2 commands:

ipconfig /release
ipconfig /renew

Wait a few seconds before typing the second command.

Also, sometimes after using bittorrent my internet connection seems glitchy for some reason. In those cases I "repair the connection" by right clicking the icon for the internet connection at the bottom right of the screen and selecting "repair connection".

That usually does the trick, and re-stabilizes my Internet connection and makes it quick again.

A couple of comments - firstly, one of the reasons that many people get download speeds that are less than advertised by their ISP is because of contention with other users 'hogging' bandwidth by file-sharing. A typical home broadband connection will have a contention ratio of 50:1, so you are already sharing your connection with up to 49 other people; it only takes a few of these to use Bit Torrent, Limewire, Azureus etc excessively and down goes your speed. Many ISPs are wise to this now, and will throttle your connection if you use P2P filesharing and may even impose penalties (including disconnection) if the abuse is too great. For this reason, it's best to limit any P2P transfers to the hours between midnight and 6am.
Secondly, most P2P software lets you limit the number of shared connections - best not to leave this as unlimited! 10 download, 5 upload is reasonable.

Hi Leo, thanks for your reply, and that interesting metaphor about me hammering my network connection with a sledge hammer! I like that visualization!

Well, the reason I have been "hammering" my network connection in such an extreme way is because it remains slow even after I close my bit-torrent client (U-Torrent). I always make sure that I select "exit completely".

And yet, even though U-Torrent supposedly closes completely, the internet speed remains noticeably slower, and more sluggish.

Interestingly, after I close the bittorrent client, and type "netstat -b" in the command line, I still see lots of open TCP connections to my computer.

So far the only thing I know that fixes the issue, is to take the drastic step and "hammer" my internet connection with the trusty sledge-hammer of "repairing Internet connection"!

Maybe my situation is unique and there's something glitchy with the way my bittorrent client is operating, or the way I set up my network? (Admittedly I'm a complete amateur at home-networking, and I only just now bought some books on networking which I started reading.)

Anyways... not sure if anyone else is experiencing this type of problem after they have opened and then closed their bittorrent client?

I've stopped using BitTorrent for the reason that it slows my computer considerably when I do. It was so bad as to make a decent, tough a little old, computer pretty much unusable. I've not stopped using P2P though. I simply switched to UTorrent.
I haven't noticed nearly the problems with slowing the computer or my internet connection that I had with BitTorrent.

AG

I find that BitTorrent and Utorrent suck. Vuze is far superior in speed and you can search inside of the program from several different bittorrent sites.

Except Vuze is written in Java.

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