According to security specialists, peer-to-peer (P2P) networks will prove a growing threat to firms during 2004, as malicious users increasingly employ them for malware attacks.

Email security specialist Clearswift has warned of the existence of a private P2P network of broadband home PCs operated by criminal gangs. The security firm said these groups have begun to deploy spam, virus writing and hacking techniques in a coordinated manner for financial gain.

The network, dubbed Sinit, removes the single point of failure often targeted by law enforcement agencies to terminate viruses - a technique used for the last Sobig virus.

Sinit offers no such central server, and each infected host becomes part of a peer-to-peer network through which additional Trojans are spread. According to Clearswift, hundreds of thousands of PCs have already been infected in this way.

Recent research by risk management specialist TruSecure suggests there will be a significant rise in malware spread by P2P file sharing in 2004. The firm estimated that almost half of the free software available on file sharing service Kazaa included thousands of planted viruses, backdoors and Trojans. "Organisations need to warn their staff about file-sharing applications and the danger they pose to them at work and at home," said Bruce Hughes, analyst at TruSecure.

TruSecure also advised firms to protect their systems against outbreaks of more fast-spreading worms akin to last year's Slammer and Blaster. "We expect there to be another big event in 2004 that causes at least $1bn of damage," said Hughes.