The Gnuman virus, seen last week, renames a copy of itself to match a P2P network user's search query term, tricking the user into downloading an executable file which then infects another machine.
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The Gnuman virus did not carry a damaging payload but shows how one could be introduced.
Eric Chien, head of the Symantec Anti Virus Centre said "This is not the first virus to affect users of peer-to-peer technology, but as the P2P phenomena grows we're seeing a new vector of infection which is difficult to screen against".
Chien said users of P2P systems such as Napster and Gnutella turned their PCs into an unsecured file server which potentially opened up the corporate network to attack from viruses or hackers.
Scott Blake, of security consultancy Bindview, said "The majority of viruses come thorough emails and any company worth its salt will screen email heavily. This type of attack, though smaller, is potentially more damaging, as traditional virus scanners are not equipped to detect these threats. For a hacker, this may prove to be a useful way of circumventing the usual security blocks placed around a network without detection".
P2P networks are growing quickly with music file-swapping site Napster claiming to have over 50 million users.
Chien's worst case scenario is an infected Napster or Gnutella user's PC on a corporate network giving undetectable access to a skilled hacker. He advises, "When using these programs there is a simple rule. Don't double click without checking the file type. If the file is an MP3 file than this will launch a compatible music player. If however, this is a new, virus-ridden executable, you will be infected and if the virus is subtle, you will probably not be aware of it."
Paul Myers, chief executive and founder of music file-swapping system Wippit, which has just launched, said, "This is worrying for users of Gnutella but not all peer-to-peer systems are the same. In our service, all the types of material transferred are scanned for both viruses and copyright clearance before they reach any of our subscribers. If there is a problem, we can also stop it from spreading."