Few people today would be unaware of the very real threat of computer viruses. Even if you're not computer savvy, the likelihood that a computer failure would affect you at some point in your everyday life is fairly high. When you use an ATM, buy groceries, swipe a credit card or drive on the roads, you are relying on the services of computers - even if you're not actively aware of it. Now I certainly don't want to alarm readers, but computer viruses can have some pretty nasty effects. So a keen awareness of viruses is important, particular for software developers.
Ignorance can be dangerous, and can give one a false sense of security.
Until recently, it was generally believed that viruses had to be written in assembly language or low-level machine code. So it was only inevitable that eventually, the Java language would be used to write viruses. Of course, the fact that it was inevitable didn't mean that the Java community saw it coming. The world's first Java virus was identified by Symantec's automated virus search engine in late 1998, and dubbed StrangeBrew. StrangeBrew could search for .class files, just like a .COM or .