Nastier than the average worm...
October's number one SirCam lost its top spot this month as the Nimda virus stormed in.
Nimda first hit servers on 18 September and can spread in three ways - via mass mailing, from server-to-server over the internet and by creating network shares within corporate IT networks.
Nimda and SirCam alone accounted for almost 50 per cent of the viruses reported this month, according to anti-virus vendor Sophos.
Nimda has managed to wreak havoc across corporations around the world despite the fact that it was only found a few months ago.
Graham Cluley, senior technical consultant at Sophos, told silicon.com: "Nimda's anonymous author only unleashed his creation in September, yet it still represented more than a quarter of reports to our helpdesk. The virus was effective because it could infect computers using a variety of techniques," he said.
Nimda was closely followed by SirCam. The worm's prolific qualities are based on its ability to change the email subject line each time it's replicated.
Also appearing on the list is Kakworm - which was originally detected back in 1999 and is still the seventh most common virus.
The full list:
1. W32/Nimda (Nimda) 27.2%
2. W32/Sircam-A (Sircam) 20.3%
3. W32/Magistr (Magistr) 12.0%
4. W32/Hybris (Hybris) 6.2%
5. W32/Apology (Apology) 3.8%
6. VBS/VBSWG-X (Homepage) 3.6%
7. VBS/Kakworm (Kakworm) 3.1%
8. VBS/SST-A (Kournikova) 2.0%
9. W32/Badtrans (BadTrans) 1.8%
10. W32/Navidad (Navidad) 1.8%