Experts say that file sharing networks are being increasingly used as a means of attacking other machines:

Computer scientists have previously shown how P2P networks could, theoretically, be subverted so that several connected PCs gang up to attack a single machine, flooding it with enough traffic to make it crash. This can work even if the target is not part of the P2P network itself.

Now, security experts are warning that P2P networks are increasingly being used to do just this. "Until January of this year we had never seen a peer-to-peer network subverted and used for an attack," says Darren Rennick of internet security company Prolexic in an advisory released recently. "We now see them constantly being subverted."

A large number of computers can easily overwhelm the servers of even large companies with data, in a so-called "distributed denial of service" (DDoS) attack. In the past, such attacks have been used by criminals to extort money from large firms.

More after the link.

Source: New Scientist