Just in time for the holidays, a worm called Dasher has hit the Internet. The malicious software, which primarily targets Windows 2000 systems, is one of three new attacks targeting Microsoft's software that has emerged in the last 24 hours. Two other recently posted attacks can crash or gum up the Internet Explorer (IE) browser.

The first reports of Dasher began circulating Thursday and two variants of the worm (http://www.f-secure.com/v-descs/dasher_a.shtml) have now been reported by Finnish security firm F-Secure.

Dasher is based on an exploit for a recently patched bug in Microsoft Distributed Transaction Coordinator, a component of the operating system that is commonly used by database software to help manage transactions. Microsoft rates the bug "critical" for Windows 2000 systems.

The worm's emergence does not come as a surprise. The "proof of concept" code that could be used to make a worm like Dasher first began circulating after Microsoft issued its patch in early October. Some security researchers feared that it could be used to create a worm similar to last August's Zotob attack, which brought down hundreds of thousands of systems worldwide.

Two variants of Dasher are now in circulation, F-Secure said Thursday. Both versions install software that then tries to infect other vulnerable systems, and that also can be used to log keystrokes and turn the computer into a remotely controlled "bot" system.

One version of the worm seems to be largely ineffective thanks to some buggy code, and other variations are unlikely to be as widespread as Zotob, said Cesar Cerrudo, chief executive officer with security research firm Argeniss in Parana, Argentina. "I don't think it will be a successful worm since that vulnerability is difficult to exploit 100 percent ... it fails 50 percent of the time," he said via instant message. However, he added, the worm still had the potential to infect thousands of systems.

Meanwhile, two IE exploits were posted to the Packet Storm (http://packetstormsecurity.org/0512-exploits/index.html) Web site on Wednesday.

The first example takes advantage of a bug in the way IE processes CSS (Cascading Style Sheet) code, according to its author Markus Heer, a developer with Penta Group, an IT consulting firm based in St. Gallen, Switzerland. CSS is a formatting standard used to give Web pages a consistent look and feel.

The bug was discovered during the course of building an enterprise Java application, Heer said in an e-mail interview. "I wrote the exploit after debugging the CSS/HTML code to find out the problem and develop a workaround for our application," he said.

The second exploit, attributed to a hacker named "Ziplock," exploits a Javascript bug to lock up an IE browser. Both this and the CSS code have been tested and found to work with version 6.0 of IE, the hackers said.

A representative of Microsoft's public relations agency was not able to comment on the bugs and an executive at the company responded to an interview request by saying he would look into the matter and comment when he had more information.