A recent string of high-profile ActiveX vulnerabilities caused theUS Computer Emergency Readiness Team (US-CERT) to advise users to disable the ubiquitous Microsoft browser plug-in technology altogether. The vectors for these recent exploits include a third-party image uploading tool used on both the Facebook and MySpace social networking sites, and flaws found in Yahoo's Music Jukebox, Real Networks' RealPlayer, and Apple's QuickTime.

"We're seeing an increase in exploits aimed at these types of tools that are commonly used with a variety of technologies including social networking sites and multimedia players. As online crime becomes more prominent, malicious actors are taking advantage of these types of vulnerabilities to accomplish their objectives," said a spokesman at the US Department of Homeland Security, which oversees the US-CERT.

Security experts contend that there's no end in sight for attacks on the plug-in architecture.

One reason is that there are plenty of security holes in ActiveX to be exploited. But another reason is not Microsoft's fault, they say: any technology used so widely will attract hacker attacks. "There's simply a lot of software out there using ActiveX that's either preloaded or embedded that users don't even realize is there, and that's why it was necessary to make the advisory," the US-CERT spokesman said.

Although features added in Microsoft's newest Web browser, Internet Explorer 7, may help reduce the problem down the road and push attackers to move on to new targets, ActiveX will remain among the leading programs assaulted by opportunistic cyber-criminals, at least for the foreseeable future, several researchers say. After all, they say, Internet Explorer's status as the most used Web browser makes it an attractive target, just as the Windows operating system has been subject to constant attack for the past decade due to its huge market share. "When hackers spend time trying to find vulnerabilities to exploit, they want to make sure that they can affect the highest number of people," said Will Dormann, a vulnerability analyst at the Carnegie Mellon Software Engineering Institute CERT.

A juicy target that's easier to exploit

When you ask researchers which ActiveX exploits make them curl their toes in reaction, the answers don't tend to focus on specific sets of attacks but instead on the sheer volume and variety of the threats, and the vulnerabilities that allow for them.

Some of the most prominent examples of ActiveX exploits include malware attacks aimed at Microsoft's Data Access Component (MDAC) software, which was pummeled for years by a broad range of attacks, and problems with the HTML Help ActiveX control module in Internet Explorer that opened it to numerous types of attacks, most notably the Phel Trojan virus.

These well-known examples are just the tip of the iceberg for the vulnerabilities that ActiveX exposes users to. One reason is that as Microsoft fixes vulnerabilities in Windows, hackers are moving to easier targets, such as ActiveX, said Randy Abrams, director of technical education at ESET, a maker of anti-malware software. "Applications and plug-ins like ActiveX are the new low-hanging fruit so that's what's being attacked," he said.

Abrams believes that ActiveX introduces unnecessary risk in many cases, because it is typically used for nonessential purposes. "The truth is that the ActiveX problem is also based on an irrational love of fashion; it's all about adding functionality to sites and applications to make them look cool, but in actuality it's completely unnecessary," he said. "If it wasn't for this need to make things look fashionable there would be much less risk." But Abrams doesn't expect developers to throttle back ActiveX use despite its security risks: "The cat is out of the bag, and sites now compete to look visually impressive and offer better functionality."