Computers running Microsoft's Windows XP are vulnerable to Trojan attacks capable of remotely controlling a user's system even when equipped with the latest Service Pack 2 (SP2) patch, security firm Symantec has warned.

The Trojan horse, called "Phel", is capable of corrupting computers visiting a malicious Web site through Internet Explorer's Help controls, according to Symantec.

The program exploits a vulnerability within Internet Explorer and SP2 that engages help files from Web pages. The vulnerability was discovered in October.

An attacker first must entice a user to visit a malicious Web site before placing the Trojan on his machine. If the Trojan is successfully launched, the malicious software could be downloaded and run on the victim's system, according to Microsoft.

A spokeswoman for the Remond, Wash., software giant said programmers were working to correct the vulnerability and will release the security update when the development and testing process is complete. She could not provide a definitive time table as to when a patch might be issued.

"Microsoft is working to forensically analyze the malicious code in Phel and will work with law enforcement to identify and bring to justice those responsible for this malicious activity," she said.

The flaw is unrelated to the three vulnerabilities in Windows reported last week by Chinese security group Xfocus. Microsoft officials were angered when the group released proof-of-concept code before sharing the information's with security vendors.