A security research firm today reported two vulnerabilities in America Online's ICQ global instant messaging service that could allow malicious attacks on the computers of more than 160 million registered users.

Available in 19 languages, ICQ launched in July 1996 as a peer-to-peer instant messaging service and has grown to include video, VoIP, and SMS features designed for young people. AOL says 80% of its ICQ users are between the ages of 13 and 29 and that the average user is connected five hours per day.

Unless users upgrade to version 5.1 of ICQ, their computers are susceptible to a vulnerability in the ICQ Pro 2003b IM client that could lead to denial-of-service attacks and remote compromise of systems, according to an alert issued by Core Security Technologies, a provider of penetration testing tools. This heap overflow vulnerability is similar to a buffer overflow: An attacker can fill an input field with too many characters and crash a PC. In the case of ICQ, attackers can add malicious data packets as part of an IM conversation.

A second Core Security alert highlights problems found in the ICQ Toolbar v1.3 that may allow attackers to control and change the toolbar's configuration settings. Another problem Core Security found pertains to the toolbar's "RSS Feeds" feature, allowing attackers to inject scripting code into the title and description fields of RSS content delivered to a user's ICQ Web page. An attacker could embed malicious code in a blog, for example, that's sent to a user via an RSS feed. "This is a fairly new form of attack, but we are seeing more and more of these," says Max Caceres, Core Security's director of product management.

Instant messaging and other client-side software will increasingly become the target of attackers because companies have focused more on bolstering the security of their backend systems and networks. "Desktops are the newest path of least resistance," Caceres says. While it would be easier for its users if AOL issued a patch for the current version of ICQ, the company is instead recommending users upgrade to version 5.1, he adds.