The software, which was posted to the Milw0rm Web site on Monday, could be a big problem for some webmasters, however the attack appears to work only on older versions of Microsoft's products. It was not immediately clear how many versions of Microsoft's products are vulnerable to the attack, and Microsoft did not immediately respond to requests for more information on the issue.
The flaw lies in the File Transfer Protocol (FTP) software used by IIS to move large files around the Internet, so the victim would have to have FTP enabled in order to be vulnerable to the attack. According to the Milw0rm post, an attacker could use this code to install unauthorized software on the server.
According to the Milw0rm poster, the code works on Microsoft's decade-old Windows 2000 operating system, while running the older IIS 5.0 server. For the attack to work, the hacker would also need to be able to create a directory on the server, security experts say.
Other versions of IIS are also at risk, according to Thierry Zoller, an independent researcher who has studied the issue. However, newer versions of Microsoft's operating systems have features that make it less serious, he added via instant message.