Security vendors are now reporting on the August virus figures, and it looks as though Mytob has topped all the charts.

Mytob variants accounted for over half of the virus infections found in August. The author of the original worm is thought to be one of the men arrested over the release of the Zotob worm.

"Mytob and Zotob may spread in different ways, but the source code is very similar," said Carole Theriault, security consultant at Sophos. 

"Moreover, the Zotob author's nickname, Diabl0, appears in more than 20 of the Mytob variants, suggesting that they may have been created by the same person.

"One thing is for sure: Mytob is still causing chaos in organisations that have not updated their virus protection and patched software vulnerabilities."

The Zotob worm itself seems to have caused little damage, and does not appear in any of the virus charts.

Elsewhere, email security firm Postini reported that phishing attacks fell sharply in August. Recorded phishing attempts were down 90 per cent on last month, indicating better filtering of likely emails. 

"Phishing is still a new enough phenomenon, so we are not surprised to see month to month fluctuations," said Andrew Lochart, senior director of marketing at Postini.

"However, the drop off in August should not give people a false sense of security and cause them to let their defences down."