Helping people with computers... one answer at a time.

BitTorrent, the peer-to-peer file sharing technology, is often suspect in computer problems. It's not BitTorrent at fault, but the files being shared.

Will using BitTorrent harm my computer, and if so and under what conditions will it?

BitTorrent itself is highly unlikely to harm your computer.

However what you download using BitTorrent - well, that's a different story. Some caution is called for.

And I know some of you are asking ... "what's a BitTorrent?"

Traditionally, when you download a file from the internet, it's really just copying a file from one computer to another. Typically that means you're copying a file from some centralized server to your computer:

Single computer downloading from a central server

The "problems" with that approach include the fact that there's a central server - if it goes down, for example, you can't download the file. Another problem is that everyone is picking up the file from one place - that means that for a popular download, that server better have a very fast or "high bandwidth" connection to the internet that all people downloading at the same time can share:

Multiple computers downloading from a central server

BitTorrent is one implementation of something called "peer to peer" file sharing. Rather than downloading from a single central server, the download is divided into pieces, and those pieces are downloaded from different computers:

Single computer downloading from multiple peers

Note that we no longer think of those computers serving up the files as "servers". Rather, they're your peers - other computers pretty much just like yours. Hence the term "peer-to-peer".

"The problem is not with the technology, but with how it's frequently used."

By copying peer-to-peer the bandwidth used is spread out across many different paths through the internet. Peer #1 might be down the street, peer #2 might be across the country, and peer #3 might be across the planet. Each will serve up parts of the file as fast as they can, and your BitTorrent client patches those pieces together as they arrive.

Now, how did those peers all get the file in the first place? The same way you're downloading it. And how did they start serving up pieces of the file? By running the BitTorrent client. One important aspect of peer-to-peer file sharing is that as soon as you've downloaded even a piece of a file, your file sharing client can then make that piece available for someone else to download from you. Your computer becomes one of the peers that can serve the file to others.

A more accurate diagram of peer-to-peer file sharing is this:

A collection of file sharing peers

In this diagram every computer interested in sharing or downloading a particular file is, effectively, connected to every other interested in that same file, sometimes called a "swarm". If a computer doesn't have all the parts of the file, it keeps asking other peers for the missing pieces until it has the complete copy. It can then remain in the swarm, making all the pieces available to any other peers that ask.

So that, in a nutshell, is BitTorrent, and peer-to-peer file sharing. In and of itself, it's just a different technology to download files, and there's absolutely nothing inherently wrong with that. BitTorrent itself will not harm your computer in any way.

But there is a problem.

The problem is not with the technology, but with how it's frequently used.

As you can see from that last diagram, there is no single authoritative site for a particular file being shared on a peer-to-peer network. If you take out any one of the computers in the network, the rest can continue to share and copy the files quite happily.

That means it's extremely difficult to stop a file from being shared.

It also means that it's very difficult to track down all the sites sharing a file.

In turn, that means that sharing illegal or pirated copies of files is much, much easier, because it's much less likely that any single sharer will be tracked down and prosecuted. Possible? Yes. But definitely more difficult.

So, many peer-to-peer networks have a lot of illegal content.

Even so, downloading illegal copies of legitimate software, music or videos won't harm your computer. It's wrong, but it won't harm you.

Spyware and viruses, on the other hand, will.

What many hackers and malware creators have realized is that there are a lot of people downloading illegal software from peer-to-peer networks. Since there's almost no accountability for what gets placed on a peer-to-peer network, it's trivial for them to put up lucrative files that have been infested with malware. For example a file sharing network might offer "Microsoft Office", and it might even be a copy of the latest and greatest copy of Office. But it's quite possible, perhaps even likely, that the person that first shared that copy added to it spyware or viruses in the hopes that people would be tempted by a free copy of an expensive product only to install much more than they bargained for.

And that's what will harm your computer - the malware that often accompanies "free" software available on peer-to-peer networks.

Because, let's face it, who would you complain to if you find that your latest free download infected your machine with spyware? As I said, there's no accountability, and nowhere to turn.

Besides the moral and ethical reasons for not downloading illegal software, the risk of infection is a very practical reason to stay legit.

Article C2825 - October 31, 2006 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

Not what you needed?

November 1, 2006 6:00 AM

If the receiving computer has a current and active firewall, antivirus, antispyware, etc. is the risk of becoming infected greater because more pieces have to be scanned? How does this compare to scanning an entire file from a single source?

Leo Notenboom
November 1, 2006 8:44 AM

I would consider it roughly equivalent. It depends somewhat on the anti-virus program's architecture and configuration. There's a theoretical hole if a virus spans two different pieces that are downloaded separately. It's a low probability to begin with, and some virus scanners may handle it anyway.

Anti-spyware scans typically kick in when (or after) you've actually run the downloaded file, so that's after the download's done regardless of how you got the file.

Firewall doesn't actually apply in this situation.

Peter Abslong
November 1, 2006 11:22 AM

The viruses/spyware myth is perpetuated by organisations who want to control what you can and can't do with your pc and everything on it.
(MPAA, RIAA and others)

If you have installed a good
- Antivirus (eg Bitdefender/kapersky)
- Firewall (not just windows xp firewall)
- Anti-spyware (eg Webroot Spysweeper)
then any potential harm is minimised.

In 10 years of downloading everything from p2p, I have had less than 5 viruses and 25 spyware. All of them detected and removed automatically within seconds my software before anything happens.

The trick is not to be stupid, read other peoples comments where possible to avoid downloading something already flagged as bad.

If retards supported and authorised by the MPAA/RIAA would stop posting fake/corrupt/spyware ridden programs on p2p then the world would be a better place. ;)

November 2, 2006 4:48 AM

no it wont harm because the only way to get a virus us for the contents downloaded from the torrent to be packed with a virus.

torrents are not like gnutella,napster or limewire where you share directly.

a torrent you have to pack the files and assign a hash to the files .

and even if someone packs a virus it will be caught by someone and then reported to the tracker and they will remove the torrent and possibly ban the poster

February 5, 2007 11:59 PM

Hi i want to destroy someones computer they have really given me a problem. They refused to pay my money. so I kindly ask you to assist me out i already have a backup of all his files as soon as he pays will return his computer normal

September 15, 2007 10:54 AM

Jack, Pick a hammer and destroy his computer. Simple! :)

January 31, 2009 1:29 PM

Two wrongs don't make a right.

May 22, 2009 12:02 AM

Can the usage of linux(ubuntu) while downloading from torrents, reduce the risk of getting virus,spywares etc??

September 13, 2009 5:29 PM

I'm terrible with technology. I've never bit-torrented anything before, but I'm curious. If I bittorrent virus-corrupted files onto one computer, then transfer those files to another computer via flash drive, would that corrupt the second computer with the virus?

It depends on a number of things, but yes, in short, it's possible. Avoid viruses, period.

Brenda Davis
November 3, 2009 7:48 AM

I used both Bit Torrent and Limewire for a little over 2 years but will never use them again. I was hit with a Trojan virus that cost me $218! Never again!

Hector Metzlbach
November 3, 2009 8:22 AM

While I don't recommend sharing/downloading pirated software, P2P file sharing is a great way to find obscure music & even old TV shows.
I've been using utorrent for a while & have never downloaded a virus. Like Peter A. states above, If you read the comments & ratings from people who have already downloaded the file you want, you should have no issues. I also use Avast antivirus & Malwarebites Antimalware.

Jerry Knowlton
November 13, 2009 6:26 PM

Just buy the software and be legal, then you don't have to worry about virus, malware and the MS secret police....

November 20, 2009 7:04 AM

i have got bittorent and i can not delete it no matter what i do i am nt the best in the world on a computer so can sum 1 plz help

January 17, 2011 2:20 PM

for those who a interested--

try using virtual machine for your downloads. thats what i do. then if you get a virus, you can just delet the virtual machine and start again. viruses in virtual machine cant harm your computer.

Before assuming that a VM is that safe, I think you'll want to read this: Does using a virtual machine keep me safer? - it can help, but there are still real risks.

February 2, 2011 1:41 PM

There's a one word answer - solution:
Or any other distro of linux.

March 11, 2011 7:44 AM

stinking utorrent was recomended to me by a friend and I had to wipe my ps3's memory becuase a file on it had a virus

November 30, 2011 3:22 AM

viruses and legitimate issues are one story, but lately i learnt another stark truth about torrents that it shortens the life span of ur hard disk. But still it is an undisputed issue.

Bogus. Torrents don't shorten your disks life.
Zwei Stein
December 19, 2011 6:14 AM

Gotta tell you that this is the first time that I have read an explanation for a computer question that I can actually understand. The words as well as the diagrams were very well put together and I do appreciate this. You see, I am the quintessential computer moron. Thank you very much for your clear, easy to understand explanation. Happy Holidays.

John Mulvihill
January 3, 2012 12:54 PM

Leo, in your opinion, is WebRoot SecureAnywhere or similar virus detection software an acceptable defense against torrent-triggered malware?

Mark J
January 3, 2012 1:22 PM

Torrent triggered malware is no different than any other kind of malware which you can get from running a virus infected program. These kinds of virus are 100% preventable if you don't run any programs or download files which are not from reputable sources.

Michael G
January 13, 2013 1:48 PM

If I'm using bit torrent to just watch movies and t.v. shows, and I have Kaspersky will I still be at risk for catching viruses? Note: I'm not using it to download software.

Mark J
January 14, 2013 12:19 AM

If you don't download programs, using BitTorrent would not put you in danger of catching a virus. However, if you use it to download copyrighted materials, you would be at risk of getting caught and paying a heavy fine. It happened to a friend's daughter.

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