A long-ignored security hole in Microsoft Internet Explorer is a gold mine for hackers, providing an easy way for them to plant malicious programs on vulnerable machines through hacker websites and instant messaging applications.
New attacks using the vulnerability include a worm that spreads through America Online Instant Messenger (AIM) and a malicious website which silently loads snooping software on victims' machines, according to independent security expert Richard Smith.
Microsoft did not immediately respond to requests for comment.
The security hole, known as the Object Data vulnerability, is in software code used by Explorer to process HTML pages containing an element called the Object Data tag.
When properly exploited, the vulnerability enables an attacker to place a malicious computer program on a user's machine. No user actions are required to infect a machine, aside from opening an e-mail message or visiting a web page rigged by an attacker.
Last month Microsoft issued software patch MS03-032, which was supposed to fix the problem. However, that patch failed to close the hole on Windows machines running Explorer versions 5.01, 5.5 and 6.0.
Earlier this month, Microsoft acknowledged there were problems with the MS03-032 patch and promised to issue a fix as soon as possible. Since then, no changes have been made to the patch, and hackers moved quickly to take advantage of Microsoft's slow response.
Recent exploits of the Object Data vulnerability include a virus which spreads over the AIM network, stealing users' account names and passwords, then mailing links to a malicious hacker website to the victim's AIM "buddies", Smith said.
Although the website associated with that threat has been removed, users who received and clicked on an infected instant message could have had their AIM account hijacked.
The vulnerability also cropped up in an e-mail message containing HTML code which exploits the vulnerability. When opened, the message installs a file called "surferbar.dll" onto the victim's computer with links to pornographic websites, according to Danish security company Secunia.
While some of the new attacks are targeting holes in the MS3-032 patch, others are targeting users who have not applied the patch at all. Short of issuing an updated patch that closed the hole, Microsoft should, at least, update its bulletin with a widely known workaround that closes the security hole, Smith said.
That fix, developed by a researcher at eEye Digital Security, requires a small change to the Windows configuration which does not appear to affect any Windows features, but would protect users from attack.
In the meantime, hackers will continue to take advantage of the Object Data vulnerability, which is easy to exploit and powerful, he said. "The sky's the limit of what you can do. This exploit is going to be used for years."
Paul Roberts writes for IDG News Service