I just found this article describing a worm that attempts to infect vulnerable Apache servers running on FreeBSD.
This doesn’t have much effect on Linux or other Unix variants (other than probably crashing lots of Apache sessions, which the machine may or may not recover gracefully from) but chances are this is just a harbinger of things to come.

You should upgrade to Apache 1.3.26 or Apache 2.0.39 immediately to avoid any problems, especially if you use FreeBSD. I’ve been running version 1.3.26 on Debian here for about a week without any issues, as I’ve come to expect from Apache.