Three virus families have become so powerful and so widespread that they account for 16 bugs named in Kaspersky Lab's Top 20 Virus report for September.

The Netsky family has eight variants in the Top 20, while MyDoom and Bagle both have four each. The only serious competition comes from the Zafi and Lovegate families, which have one a piece.

Kaspersky analysts say September didn't hold any major surprises.

''This September we witnessed several outbreaks caused by new variants of our old enemies Bagle and Mydoom,'' reports a spokesman for Kaspersky. ''Thankfully, we did not see any malware exploiting the JPEG vulnerability in MS Windows, despite dire predictions by some analysts that an outbreak was inevitable. In short, September resembled August, with only minor changes.''

What was remarkable about September is the fact that it's the first month in 2004 that didn't rank any viruses from 2003 in the Top 20 list. Sobig-F and Swen finally have dropped off the list.

''Netsky variants continue to dominate the top slots; changing places with each other, but not yielding to any other viruses,'' reports Kaspersky analysts. ''NetSky-Q pushed aside NetSky-AA and took first place.''

The top 10 viruses in the Kaspersky ranking are: Netsky-Q, Netsky-AA, Zafi-B, Netsky-B, MyDoom-M, Bagle-Z, Netsky-D, TrojanDownloader.JS.Gen, Netsky-T and Netsky-Y.