Cisco Systems has written to users to warn against forged messages containing computer viruses which purport to come from its Product Security Incident Response Team (PSIRT).

Several forged virus bearing emails apparently from psirt@cisco.com have been sent out, one of which (containing an infected attachment 'width.pif') was received by The Register this morning. These messages are not authentic and can be safely ignored, Cisco advises.

Cisco is "aware of these emails and is actively looking at solutions to reduce or eliminate the forged messages", it said in a notice to subscribers of the list this evening.

Authentic Cisco messages on the moderated mailing list can be identified by a PGP signature and will originate from a verified "cisco.com" address, it advises.

Similarly spoofed email messages infected with the Klez virus have forced AV vendor Sophos to deny (http://www.sophos.com/virusinfo/articles/klezh2.html) any responsibility in the wider distribution of the virus.

The recent Klez-H (http://www.sophos.com/virusinfo/analyses/w32klezh.html) worm uses its own SMTP engine, and can appear to have come from any email address, it advises.

Some of its other customers have also reported receiving an unsolicited email apparently from Sophos claiming to contain disinfection tools for the W32/ElKern (http://www.sophos.com/virusinfo/analyses/w32elkernc.html) virus.

These emails contain a copy of the Klez-G worm and, again, do not originate from Sophos, the company states.

Sophos recommends that users do not open or launch unsolicited executable attachments and keep their anti-virus software updated.

Computer users are also advised to consider installing a patch from Microsoft (http://www.microsoft.com/technet/security/bulletin/MS01-027.asp) which should fix a vulnerability in some versions of Outlook, Outlook Express, and Internet Explorer that is exploited by Klez-H and a number of other viruses.

After a slow start, spread of the Klez-H worm has reached near epidemic proportions. Managed services firm MessageLabs reports blocking more than 200,000 virus infected emails destined for its customers (http://www.messagelabs.com/viruseye/report.asp?id=100), since the virus first appeared last week. ®

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