It is true - it's all to easy for someone to hack a computer if the owner isn't paying attention.The proliferation of DSL and other 'always on' ISPs has made the problem that much more dangerous.
I've been hacked - on a previous DSL based computer, we got sloppy and at some point or another wound up with a 'backdoor' virus, which gave anyone with the counterpart program unlimited useage of our computer. Fortunately, it appeared that the hacker in question only was interested in using our computer as a "zero day" source to distribute MP3 files, but he could very easily have set us up as a satellite to use for ANY number of nasty shenanigans.
There are a number of programs that take advantage of MS security flaws. MS is FAMOUS for being about as secure as a sugar sponge in a rainstorm, and the new programs are likely to have the same problems. AOL is a similar risk. Even more fun, I recently found out that someone using "ICQSniffer" can apparently hack into your computer using your ICQ connection. Whee!
M