Top ten viruses: Old pretender still number one

The SirCam virus is the world's most prevalent virus for the second month in a row, and is responsible for half of the world's infections.

The email virus continues to top the charts because it is programmed to constantly change its name, making it hard to detect. This is despite the fact virus companies have had patches for the bug out since mid-July.

The virus also makes detection more difficult by generating its own email client, a feature which has enabled it to skip past some email gateway defences.

Graham Cluley, senior technology consultant at Sophos, said the virus could now be counted among the top five viruses of all time. However, he added: "Unlike the Lovebug or Melissa it didn't hit hard when it was first released, but now is still around in huge numbers months later."

He said eradication of the virus was made difficult by the lack of a simple message for the media and computer users to latch onto in describing the virus, meaning many have failed to spot it.

When executed SirCam picks out potentially confidential files from a user's 'My Documents' folder and emails them to contacts from the Outlook address book.

Sophos's figures for August show SirCam is responsible for 49.8 per cent of all infections. Other firms put the figure higher - similar research from MessageLabs puts SirCam's incidence at 59 per cent.

The month's number two virus, Magistr, has also been around for some time, having been first reported six months ago. Sophos's Cluley said: "You begin to ask just how many times to I need to say this before people start taking these threats seriously."

He urged users to update their anti-virus software.

The much-hyped Code Red virus was not reported widely this month. It was responsible for just 1.2 per cent of recorded virus attacks.

The full Sophos list is as follows:

1. W32/Sircam-A (Sircam) - 49.8 per cent
2. W32/Magistr-A (Magistr) - 13.0 per cent
3= Unix/Sadmind (Sadmind) - 3.6 per cent
3= W32/Hybris-B (Hybris variant) - 3.6 per cent
5. W32/Apology-B (Apology variant) - 2.6 per cent
6. W32/Flcss (Funlove) - 2.3 per cent
7. VBS/Kakworm (Kakworm) - 2.1 per cent
8. WM97/Ethan (Ethan) - 1.4 per cent
9. W32/Code-RedII (Code Red Trojan) - 1.2 per cent
10. VBS/Haptime-A (Happy Time) - 1.1 per cent