Klez makes it to the top of the charts

Stubborn mass-mailing worm Klez has officially been named as the number one virus of the year.

Discovered in April, Klez deletes files on local and network drives and overwrites other files with random data, making them impossible to restore.

Antivirus firms confirmed that Klez topped the charts for the year. Sophos said that it accounted for almost one in every four infections, and McAfee said that it was easily responsible for the highest number of infected files.

But for home PC users threats will come from online file sharing services such as Kazaa, which can lead to people downloading 'Trojan horse' files that give hackers remote access to their PC.

"The emergence of broadband this year has led to increased file-sharing and that increases the number of viruses shared," said Jack Clark, product marketing manager at McAfee.

Graham Cluley, senior technology consultant at Sophos, urged PC users to be wary of suspicious email attachments.

"Viruses aren't going away," he said. "Take some responsibility for the data on your home computer. If you're not expecting an email from someone don't double click on it to see if it is dangerous or not."

Clark explained that users should take time to research the subject of security and educate themselves about the threats.

Virus attacks on mobile phones and personal digital assistants (PDAs) are not expected to materialise next year, according to the experts.

McAfee indicated that the market for these devices is not yet large enough to be attractive to attention-seeking virus authors, while Sophos pointed out that it had not come across a PDA virus since one written for Palm Pilots three years ago.