A security flaw in Media Player 7 lets unauthorised users run arbitrary code on a victim's PC if the latter is viewing a Web site or accessing an HTML email.

The discovery was made by GFI, a developer of email content-checking software. Microsoft has been notified and has issued an advisory which you can view here.

All that is required, GFI security engineer Sandro Gauci says, is for an email be opened on a machine which includes Windows Media Player 7 and on which HTML scripts are allowed, or by browsing a malicious site.

He went on: "This security problem is exploited by embedding a JavaScript (.js) file within a Media Player skin file (.wmz) which can also be embedded in a Windows Media Download file (.wmd). This does not require the user to run any attachments since the Media Player file is automatically executed using an iframe tag or a window.open() with in a script tag."

To avoid the problem, GFI advises users to filter incoming emails for WMD and WMZ files. The company says the following should also be removed from incoming HTML emails: JavaScript, iframe tags, meta refresh tags and possibly ActiveX tags. ®