ActiveX controls made up most of all browser plug-in vulnerabilities in the second half of 2007, according to Symantec.

The company has just released its semi-annual web security report and in it said that Microsoft's technology, primarily used to create add-ins for Internet Explorer, accounted for 79 percent of the 239 plug-in bugs discovered between July and December 2007. The plug-in with the next-highest number of flaws was Apple's QuickTime, which had just 8 percent of the six-month's total.

Only one vulnerability in a plug-in for Mozilla's Firefox browser was detected in the same period, meaning Firefox's extensions - the moniker Mozilla uses for plug-ins - accounted for only 0.4 percent of all found flaws.

Symantec argued that ActiveX's poor showing could stem from several factors, including the availability of "fuzzing" tools that hackers can use to sniff out input vulnerabilities in the controls. But it also fingered several traits inherent to the add-on technology.

"ActiveX is also an attractive target because many users may not be aware that they have installed vulnerable controls, and because of the relative difficulty of removing or patching ActiveX controls once they have been installed," said Symantec in its Internet Security Threat Report Volume XIII (download PDF). Hackers also root out ActiveX bugs, Symantec continued, because they are used exclusively on Internet Explorer (IE), which still holds nearly 75 percent of the browser user market.

The 2006 launch of IE7, which Microsoft touted as much more secure than its predecessors, hasn't had a measurable impact on the number of ActiveX vulnerabilities, Symantec's report said, even though the newer browser introduced several security features designed to stymie plug-in abuse. In the second half of 2007, Symantec detected 190 ActiveX vulnerabilities, down about 10 percent from the 210 found in the first six months of that year.

"This may be a measure of the effectiveness of these security enhancements or it may indicate that many at-risks users have not upgraded to Internet Explorer 7," Symantec speculated.

In the case of enterprises, the latter may be the cause, according to other research. By the end of 2007, Forrester Research recently said, only about 30 percent of the 50,000 corporate computer users it surveyed said they were using IE7; the bulk of the remaining 70 percent reported using IE6.

The upshot, said Symantec, is that ActiveX remains a major problem. "While Microsoft has gone a long way to improve the security of Microsoft Windows and its applications, ActiveX is still a critical security exposure on the Microsoft Windows platform," its report said.

ActiveX's problems haven't improved in 2008. In February, for example, a wave of vulnerabilities in several high-profile ActiveX controls prompted the US Computer Emergency Readiness Team (US-CERT) to recommend that users disable all IE plug-ins.

Apple's QuickTime media player took second spot in Symantec's plug-in hall of shame list. During the last half of 2007, the security vendor discovered 19 vulnerabilities in QuickTime, an increase of just one from the 18 in the six months before that.

The plug-in, which runs on both Windows and Mac OS X, hasn't been given any grace so far this year either: Apple has had to patch the program three times since January to fix 16 flaws.

Other plug-ins for which Symantec tallied vulnerabilities included Java (13 flaws detected), Adobe's Flash (11), Microsoft's Windows Media Player (4) and Adobe's Acrobat Reader (1).