The worm is thought to be capable of spreading only to Web servers running the FreeBSD operating system, an open-source variant of Unix, that haven't had a patch applied for the recent flaw. Although few people have reported the worm, it is thought to be infecting vulnerable Web servers worldwide.
"It is spreading," said Domas Mituzas, a systems developer for Baltic information-technology firm Microlink Systems and the first to report the new worm. "It hit us from Poland, and the comments are in Italian, so it could be from any part of the world."
From his early analysis of the worm, the 19-year-old Lithuanian programmer believes it was designed to create a flood net--a collection of compromised servers that can be used in a denial-of-service attack to overwhelm a target with data.
While the initial advisory on the flaw, which was found by network security firm Internet Security Systems, said the Apache hole was exploitable only on the Windows version of Apache, a hacking team called Gobbles later claimed that the flaw could be exploited on all versions of the program. The team released exploits for Apache running on various versions of BSD to prove its point.
That probably helped the creator of the worm do the work, Mituzas said. "Otherwise, it would be really astonishing that someone had been able to write an exploit so fast," he said.
Marc Maiffret, chief hacking officer for network protection firm eEye Digital Security and one of the key analysts of the , agreed that the Apache worm was creating a stable of servers, sometimes called zombies, for later use in an attack.
"It's definitely setting up its own flood net," Maiffret said, but he added that "something even more destructive" could have been included in the worm.
There are 10.4 million active Web sites running on the Apache server, according to British consulting firm Netcraft. While the fraction of those servers running on FreeBSD is a minor share of the BSD, Linux and Unix market, both Mituzas and Maiffret warned that whoever created the worm could modify it to attack Apache running on any version of BSD and potentially Linux, Solaris and Unix.
At present, if the Apache worm tries to spread to any non-FreeBSD system, it will likely crash the session on the server to which the worm had connected. That's not so bad, said Maiffret, but it could cause many servers to crash if the worm develops into an epidemic.
"If the worm keeps hitting you, then it will keep dropping sessions, and it will be similar to a denial-of-service attack," Maiffret said.
The worm does not yet have a name.