Yaha-E displaced Klez as the most common viral menace on the Internet over the last month, according to Messagelabs.

The managed services firm has blocked Yaha-E 367,158 times so far in July, relegating Klez-H (332,343 interceptions) to second place in its monthly viral charts. Sobig-E (blocked 188,235 times) and BugBear-B (108,206) and Sobig-A (63,076) make up the remaining stop five places in MessageLabs chart, released last night.

The company reports that one in 166 emails processed this month contained a virus, about average for this time of year.

None of the viruses that make up MessageLabs top ten chart are new. While fewer in number, backdoor-trojans are increasing appearing on MessageLabs' anti-malware radar screens.

"In recent months, an emerging trend has also been observed in the distribution of backdoor-trojans via email, typically sent as an attachment to spam emails in very large volumes. Typically these trojans are being altered and redeployed, almost on a daily basis so as to sneak past anti-virus software," MessageLabs reports.

For example, in July MessageLabs intercepted the following patterns of variants for the same trojan, in almost as many days: Downloader.DI!Eloan (1,083 interceptions), Downnloader.DI!WFd7f3 (589), Downloader.DI!Heloc (522) and Downloader.DI!WF97bc (110).

The company also operates an anti-spam service. In July, 79.7 million of the 156.6 million emails - just over 50 per cent - scanned by MessageLabs' Anti-Spam service turned out to be junk mail. ®

Top ten viruses blocked by MessageLabs in July

1. Yaha-E
   
2. Klez-H
   
3. Sobig-E
   
4. BugBear-B
   
5. Sobig-A
   
6. Yaha-K!e2a2
   
7. Klez-A
   
8. SirCam-A
   
9. Yaha-P
   
10. Ganda-A

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