Microsoft has shifted its Hotmail anti-virus contract from McAfee to Trend Micro.

Under the agreement, Trend's anti-virus technology will scan inbound and outbound attachments for viruses, worms and Trojan horse programs on all of Hotmail's 187 million accounts. McAfee had provided anti-virus scanning for MSN customers at least since 2000.

Trend is based in Tokyo and makes the PC-cillin desktop anti-virus and content security products, including PC-cillin Internet Security, a suite of anti-virus, firewall, anti-spam and content filtering products.

The company would not comment on the criteria MSN used to select its product for Hotmail, or the size of the deal, citing instructions from Microsoft. Ease of integration between Trend's systems and back-end servers used by MSN for Hotmail was an issue however, said Punit Minocha, senior director of business development at Trend. "Our engineers were out there in early discussions with Microsoft, and helped them resolve the issue. I think that had some bearing on the decision."

Trend's anti-virus scanning engine will run on Hotmail servers and be tightly linked to Trend's virus definition update servers.

Trend has long been the number-three anti-virus software provider, behind Symantec and McAfee. Sales to corporations has always been its strong suit, but the deal with MSN could boost its share of the consumer anti-virus market.

The announcement is more bad news for McAfee, which lost ground in both the home and corporate anti-virus market last year.