Using IE is like walking around with a "Kick Me" sign on. Same goes for using Outlook (email client) and its deformed offspring, Outlook Express. They've got more holes than swiss cheese, and by virtue of their vast deployment, they're by far the favorite target of virus and malware writers.
Earlier this year, the Department of Homeland Security actually issued a warning advising people to use browsers other than IE. That's a pretty serious statement as to how unsafe IE is:http://www.internetnews.com/security/article.php/3374931
Many people in IT (myself included) have been advising anyone who would listen not to use IE for security and technical reasons *for years*, to little avail. That the US government has finally figured this out is truly a demonstration of how obvious this point has become.