An international hacking contest scheduled to begin this weekend could cause headaches for organisations worldwide and disrupt the Internet, according to a warning from Internet Security Systems (ISS).

The contest, known as the Defacers Challenge, awards points to malicious hackers who successfully compromise an organisation's Web server and deface its Web pages.

ISS first became aware of the contest last week by monitoring Web sites and Internet Relay Chat (IRC) channels frequented by malicious hackers who specialise in defacements, according to Peter Allor, manager of X-Force Threat Intelligence Services at ISS.

Rather than focusing on the volume of defacements, the Defacers Challenge is set up to reward the skill of malicious hackers who can compromise systems running obscure operating systems such as Apple Computer's Macintosh and Unix variants such as IBM's AIX and Hewlett-Packard's HP-UX.

Contest organisers even set up a Web page that outlines the rules of the game, including a point system for compromised machines (Windows: 1 point, HP-UX and Macintosh: 5) and what guidelines for what counts as a valid defacement.

The target is to deface 6000 Web sites. A prize of free Web site hosting is offered to the malicious hacker who can reach that goal first or accumulate the most Web sites in trying to do so, according to information posted on the site.

The Challenge is scheduled to begin on July 6 and last for six hours, though information on the exact time of the Challenge has not yet been released, Allor said.

ISS does not know which hacker or group of malicious hackers is responsible for organising the challenge.

While the contest and Web page may be a joke, ISS noticed an increase in reconnaissance and probing scans of Web sites that may be connected to the contest, Allor said.

Malicious hackers may be scouting out high-value systems, or even compromising them in advance so that they can quickly be defaced once the contest begins, he said.

ISS recommends that organisations deactivate unneeded public-facing Web servers and turn off unnecessary services on Web servers that are needed, in addition to applying any necessary software patches to potentially vulnerable machines, Allor said.

Recently disclosed software vulnerabilities that have not yet been patched are attractive targets for hackers, he said.