Microsoft has revealed its web browser spam filter technology has stopped its one-billionth piece of malware from being downloaded.

Internet Explorer 8's (IE8's) SmartScreen Filter uses URL reputation-based anti-malware technology to warn users if they are visiting web sites hosted by servers known to distribute unsafe content.

James Pratt, Internet Explorer business and marketing senior product manager, said the milestone was evidence of continued investment in the browser’s back-end service since IE8 was released in March 2009.

“Your browser needs to continually enhance and improve its service,” noted Pratt in a blog posting. “We have got better and better at blocking malware through the SmartScreen Filter.”

Pratt was also quick to point to figures from Net Applications released last week that gave IE8 a total browser market share of nearly 26 per cent.

The last milestone for SmartScreen Filter was announced in August 2009, when Microsoft said 80 million malicious downloads had been blocked.

Rik Ferguson, senior security advisor for Trend Micro, told V3.co.uk that, by comparison, his firm’s Smart Protection Network received 45 billion daily requests and blocked 4.3 billion queries a day.

“Out technology works in a similar fashion to the SmartScreen blacklists,” he said. “But it works across emails, URLs and other malware files because all threats operate on multiple vectors.”

Like Ferguson, senior technology consultant for Sophos Graham Cluley conceded that it was good to see browser software developers like Microsoft and Mozilla add more malware protection in at the back end for users.

“More and more malicious software is distributed via the web,” Cluley said. “Technology like the SmartScreen Filter is a good thing because many users don’t keep their anti-virus software up-to-date.”

But he added it was no substitute for full anti-virus software protection.