It used to be that an IT administrator could warn employees about opening attachments from unknown sources or clicking on links from unknown e-mail senders as the first line of defense against spam, malware, and other bad stuff on the Internet.

Today, the seedy side of the Internet comes in many different forms and from many different sources. Stop for a moment and think about the new places where malware might be buried, hidden, released, and shared--a legitimate site that's been hacked, a b...