The firewall in Microsoft Windows Vista can be compromised to perform prohibited functions, according to new research by Symantec.

This is likely to cause embarrassment to Microsoft, which touted Vista as its most secure platform to date and implemented a plethora of new security features, including an improved firewall.

The software giant’s operating system is, by default, configured to block all third party and unknown network communications, unless the user clicks on the unblock button, said Orlando Padilla, from Symantec’s security response team, in a blog on the company’s website.

Padilla, who conducted the study released last week, said the problem concerns the unblock button, which may be accessed by someone with the same privilege level as a standard user. This configuration of privileges creates a vulnerability in the firewall’s policy, which can be exploited by an attacker to code malware, he said in the post.

“[The firewall] poses a great limitation for malicious code looking to back door a host. In effect, malicious code can automate the unblock process by simply sending a message to the firewall pop-up dialog box via the SendMessage API call,” Padilla said in the web entry.

Microsoft could not be reached for comment.