Kama Sutra worm crashes malware chart

The return of the 'trash your PC' virus

Virus authors were hard at work last month creating 2,312 new malware variants - a third higher than December, according to UK-based security firm Sophos. Most of these attacks were financially motivated and designed to steal sensitive information from compromised PCs.

But it was the return of an old-school "trash your Windows PC" worm that captured the most headlines. The Kama Sutra worm (AKA Nyxem-D or Blackworm) first appeared on 18 January posing as an email message offering a variety of salacious content. Users daft enough to fall for this ruse wind up with an infected machine and disabled security software. Worse still, Nyxem-D is also programmed to overwrite files on Friday 3 February.

According to SoftScan, a Scandinavian email filtering firm, levels of infection in the UK and the majority of Europe are very low. The largest number of infections by far is in India, it reports.

Even so Nyxem-D appears at number four in Sophos's chart. Sober-Z remains January's most frequently encountered virus but since the worm is programmed to stop spreading after 6 January it ought to drop off the radar completely in February even though it's doubtless numerous machines will remain infected. Sober-Z stopped spreading in the first week of January but still racked up almost 45 per cent of malware reported to Sophos last month, a stat that illustrates the potency of the attack it unleashed. Sophos reckons that 1.4 per cent or one in 70 emails was viral in January.

Malware laced with offers of smut, as used by the Kama Sutra worm, is a common trick. Another more sophisticated type of attack appeared last month. The Brepibot virus posed as a request for the recipient to check the article and photo for editorial content before it is used in a high profile publication such as the Guardian's Business section. The malware was spammed out with the UK in particular and the US, to a lesser extent, bearing the brunt of the assault, according to SoftScan.

January saw many variants of the Feebs worm emerging. Although none of them got anywhere near the prevalence of the Kama Sutra worm and the like, Feebs was technically sophisticated. Among other features (rootkit, P2P propagation, reporting via ICQ, on-the-fly injection into emails sent by the infected user), the worm uses Javascript to spread, according to an analysis by security appliance firm Fortinet. The worm lies in an encoded string of a Javascript embedded into an .hta document. Whenever run, the Javascript decrypts the worm body, and executes it. The .hta document is then regenerated and bulk mailed to potential victims. ®

January top ten virus chart, as compiled by Sophos:

1. Sober-Z
2. NetSky-P
3. Zafi-B
4. Nyxem-D
5. Mytob-BE
6. Mytob-FO
7. NetSky-D
8. Mytob-EX
9. Mytob-C
10. Mytob-AS