If you are running an Apache server you should immediately download the latest patches from www.apache.org. A big security exploit was discovered a few days afo:

Versions of the Apache web server up to and including 1.3.24 and 2.0
up to and including 2.0.36 contain a bug in the routines that deal with
requests encoded using chunked encoding. This bug can be triggered
remotely, and this functionality is enabled by default.

Due to the existence of exploits circulating in the wild for some platforms, the risk is considered high. The Apache Software Foundation has released versions 1.3.26 and 2.0.39 that address and fix this issue, and all users are urged to upgrade immediately. These versions are available for download;

[from apache.org]