Many people fault Microsoft but the truth is, they are a big target. The most prolific virus to date has been the Melissa virus which hit last April. It was a macro virus that hit the world via email and brought thousands of computers to their knees. The Chernobyl virus did the very same thing as did the Explore. A battle is going on with virus writers trying to make their viruses harder for anti-virus software to detect and virus companies trying to detect and eradicate all the new variations hitting them on a daily basis.
Most writers are often computer programmers who want to show off their programming prowess.
They write them for attention but very few virus writers release them into the wild. And don't think they are all nerdy kids. The writer of the Melissa virus was 30 year old David L. Smith who faces a long prison term for his misdeeds. Be prepared 1. Don't open any attachments from people you don't know 2.