A new type of bot being operated out there on the Internet, now interestingly enough is using Web Servers for initiating a DoS (Denial of Service) attack, as opposed to home or business PCs.
The notion is that since web servers have high-speed connectivity to the Internet vs. your average home PC, better to compromise a single web server for a DoS attack rather than 50 PCs.
More can be read on this here on CNet: New DoS attack uses Web Servers as Zombies