Thomas Reifferscheid discovered that adzapper, a proxy advertisement zapper add-on, when installed as plugin in squid, the Internet object cache, can consume a lot of CPU resources and hence cause a denial of service on the proxy host.
The old stable distribution (woody) does not contain an adzapper package.
For the stable distribution (sarge) this problem has been fixed in version 20050316-1sarge1.
For the unstable distribution (sid) this problem has been fixed in version 20060115-1.
We recommend that you upgrade your adzapper package.