A wave of bugs in the plug-in technology used by Microsoft's Internet Explorer (IE) browser has some security experts, including those at US-CERT, recommending that users disable all ActiveX controls.

The US Computer Emergency Readiness Team (US-CERT), part of the federal government's Department of Homeland Security, put it bluntly in advisories posted in the last two days: "US-CERT encourages users to disable ActiveX controls as described in the Securing Your Web Browser document," the organization recommended.

US-CERT's advice was prompted by multiple vulnerabilities in high-profile ActiveX components used by members of the popular Facebook and MySpace social networks, as well as users of Yahoo's music services.

Three new vulnerabilities in the photo uploader software used by both Facebook and MySpace were disclosed Monday by researcher Elezar Broad, who on Monday also posted sample attack code for a pair of critical bugs in Yahoo's Music Jukebox. Last week, Broad had pinned the Facebook and MySpace ActiveX controls with two other flaws. All five of the Facebook/MySpace vulnerabilities originated with an ActiveX control developed by Aurigma Inc.

As the number of vulnerabilities mounted, security professionals began ringing the alarm. On Monday, for instance, Symantec analysts urged users to "use caution when browsing the Web" and told IT administrators to disable the relevant ActiveX controls by setting several "kill bits" in the Windows registry.

US-CERT, however, offered up more aggressive advice as it recommended users move IE's security level to the "High" setting, which completely disables all ActiveX controls.

Setting IE's security level to 'High' disables all ActiveX controls. To get here, select Internet Options from the Tools menu, then click on the Security tab. Click Internet at the top for the zone, then move the slider up to the maximum.

"That's the easiest way to protect yourself," agreed Oliver Friedrichs, director of Symantec's security response group. "But it can also have an adverse impact on your browsing experience." A compromise, said Friedrichs, would be to disable "only those plug-ins that pose a current and imminent threat," such as the flawed ActiveX controls used by Facebook, MySpace and Yahoo.

Disabling individual ActiveX controls, however, requires editing the Windows registry, a task too scary for most consumers to contemplate.

Not so in business. "That approach is hard to argue against in the enterprise," said Friedrichs, who noted that there are tools available that let corporate IT administrators push registry changes -- including new keys that disable specific ActiveX controls -- to all users.

The SANS Institute's Internet Storm Center acknowledged that setting kill bits is beyond the ken of most users; one of its researchers came up with a graphical interface-based tool that sets and clears the kill bits of six ActiveX controls that have been tagged with bugs in the past week. The free tool can be downloaded from the ISC's Web site.

The SANS Institute's free 'kill bit' tool provides checkbox-simple settings to disable half a dozen ActiveX controls. It's much easier than monkeying with the Windows registry.

"This is an easy way to disable the ActiveX control [for people] who don't know how to modify the keys directly," said Friedrichs.

As if to emphasize the seriousness of the ActiveX problem, Friedrich's team warned customers Monday that attack code targeting one of the two Yahoo Music Jukebox bugs was on the loose. "Just one day after the proof of concept was released, in-the-wild exploitation was identified in our crawler honeypots," Patrick Jungles, a Symantec analyst, said in an alert to customers of the company's DeepSight threat network.

Browser plug-in problems are anything but rare, said Friedrichs. "In the first half of 2007, Symantec counted 237 plug-in vulnerabilities. That's compared to 108 in all of 2006." The vast majority of those bugs -- 89 per cent in fact -- were in ActiveX controls, making IE by far the most popular target for plug-in exploits.

Last week, Facebook and MySpace said that they had come up with fixes for the vulnerabilities Broad had initially spotted, saying through a spokeswoman that they were "working to individually alert users of any additional steps that need to be taken to ensure user security." The two companies did not immediately respond to queries Tuesday about the newest bugs, however.

As of mid-day Tuesday, Yahoo had not yet replied to questions posed the day before concerning the Yahoo Music Jukebox flaws.