Another new Internet worm is spreading by exploiting a flaw in the Sasser worm.

Tentatively named Dabber, it takes advantage of a vulnerability in an FTP server component in the Sasser worm and may have infected thousands of computers infected with Sasser. Dabber is believed to be the first worm that spreads specifically by targeting a flaw in another worm's code, according to an advisory published by LURHQ.

The worm uses code written to exploit the FTP flaw and was recently released on the Internet, scanning the Internet on port 5554 for computers running Windows and infected with Sasser, LURHQ said.

When it finds vulnerable hosts, it connects to the victim and uses a built-in FTP server to transfer the worm file, named "package.exe", to the system. When run, the Dabber worm installs itself on Windows, shuts down the Sasser worm and other worm processes, then prevents them from running again.

But it also opens TCP port 9898 as a backdoor, which can be used to download other code or communicate with the infected host, LURHQ said. Dabber did not appear to be spreading quickly Thursday, but the number of infections was escalating, LURHQ said.

However, we should sound a note of caution. The very high-profile security issues over the past few months have had a noticeable effect on how security companies deal with, and make public, their discoveries.

Only Panda of the big security companies has become concerned about Dabber, and it damaged its hard-fought for public profile last week by prematurely denouncing the theory that the Sasser worm was written by one person on the basis of circumstantial evidence.

There is a growing trend of over-blowing security issues in order to garner headlines and public attention, something that is especially prevalent with Microsoft security issues. Although, ironically, the relationship with Apple appears to be the other way around.

Sasser appeared on 1 May, and exploited a recently disclosed hole in a Windows component called the Local Security Authority Subsystem Service, or LSASS. Microsoft released a software patch, MS04-011, on 13 April.

Dabber is similar to Sasser and earlier worms like Blaster because users do not need to receive an e-mail message or open a file to be infected. Instead, just having a Sasser-infected Windows machine connected to the Internet is enough to catch Dabber.

Last week, Microsoft acknowledged that more than 1.5 million copies of a Sasser cleanup tool were downloaded from its website within the first 48 hours after it was offered.