An Xmas-themed worm has hit the Internet.

"Dasher" targets Windows 2000 and is one of three new attacks targeting Microsoft software that have emerged in the last 24 hours. Two other recently posted attacks crash Internet Explorer.

The first reports of Dasher began circulating Thursday and two variants have now been reported by 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 is not 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.

Both variants 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, CEO of security research firm Argeniss. "I don't think it will be a successful worm since that vulnerability is difficult to exploit. It fails 50 percent of the time," he said. However, the worm still had the potential to infect thousands of systems.

Meanwhile, two Explorer exploits were posted to the Packet Storm website earlier this week.

The first takes advantage of a bug in the way Explorer processes CSS code. It was discovered during the course of building an enterprise Java application. The second exploits a Javascript bug to lock up Explorer.

And just in case you're wondering, Dasher is just one of Santa's reindeers - the others being: Dancer, Prancer, Vixen, Comet, Cupid, Donner, Blitzen and Rudolph.