Microsoft will release an anti-phishing filter for Internet Explorer months ahead of its original schedule.

The company had originally planned to release the security filter in Explorer 7.0, due next year, but the appearance of rival add-ons for both Explorer and rival browsers such as Mozilla’s Firefox have resulted in a change of heart.

A preliminary version could now be offered as a free plug-in for the MSN toolbar as early as a few weeks from now, the company’s anti-spam and anti-phishing strategy manager, John Scarrow, has indicated.

The software will use the now well-established technique of analysing a website domain, and the address variables, to decide whether it is legitimate or not. This approach is already used by a number of add-ons for Explorer and other browsers.

If a visited site is on a known list of suspect domains, or is believed to be spoofing a legitimate domain, the user will be alerted though a series of colour-coded alerts.

The plug-in will require users to be running version 6.0 of Explorer, and to have updated Windows XP with the SP2 security update. It is not clear when or if other users will be able to access its features at a later date.

It is not believed that it will be able to counter more sophisticated techniques such as key-logging, however, which raises the likelihood that these features will be added when Explorer 7.0 eventually appears.