Claranet, the leading British ISP, this week abandoned its first line of defence against email-borne viruses following performance issues with its in-house developed technology, its global mail filter.

Claranet continues to market to business users a separate service which uses more sophisticated virus scanning and filtering. Other ISPs sometimes bundle such services with basic access packages targeted at consumers - for example, BTOpenworld this month rolls out virus/spam blocking technology from Brightmail/Symantec to improve the customer online experience.

Claranet takes a different line. Since the decision to drop its global mail filter, the ISP advocates a DIY approach - advising home users to use desktop AV scanners (which they should use anyway) and to set email clients to automatically delete email from persistent virus senders.

Claranet introduced a global mail filter to protect customers from infection by the prolific Anna Kournikova virus. Email headers were searched for filename attachments associated with viruses. If a virus is detected the software returns a message to the sender with a note informing them of the infection.

This worked well during the Anna K outbreak but with many new viruses using spoofing the technology is becoming more trouble that it's worth, prompting a decision (at least for now) to sideline it, the ISP says.

Neil Levine, Claranet CTO, explains: "Claranet has over the years applied generic filters to our mail spool to prevent mails which may be virus infected being delivered. However, as a result, there was a strong potential for false positives to be generated, which may have meant valid, non-infected mails were filtered out."

"After consulting with customers on our newsgroups, the global filters were removed after customers stated they preferred to control the type of filtering themselves, either using Claranet's User Mailfilter facilities or by using locally installed software on their PCs.

"Any virus in the future which causes service degradation will continue to be filtered." ®