IT security firm McAfee has revealed a malware outbreak that has affected 500,000 file-sharing computers.

According to a report on itpro.co.uk, McAfee claims it has detected a Trojan horse that masquerades as a media file, in what it describes as the most significant malware outbreak since 2005.

It is claimed that peer-to-peer download sites such as Limewire and eDonkey have had the malicious mp3 and MPEG files spread through them. However, it is believed the threat is "medium level" because it is an adware as opposed to spyware infection.

Toralv Dirro, security strategist at McAfee COMMA said: "We are currently seeing that the distribution is still going on. It is now at about 580,000 where files have been detected, so people are continuing to download and share these files."

He added that in future hackers may copy the method but with potentially more sinister motives.

In related news it was revealed last month by the Department for Business, Enterprise and Regulatory Reform that UK businesses' IT services had experienced a ten-fold increase in computer hacking attacks over two years.