I'm a rookie knife maker but a veteran at computer security. Threats hitting you on the Internet are fairly random (like parking your car on the street). Right now, the problem is money. If the bad guys can control 10,000 computers (owned by you and others) they can rent them out for spammers, denial of service extortion rackets, fee forward scams, and Phishing. Typical rates for a "bot net" are in excess of $100 per hour.
The profit is why the world is seeing more of this activity. I also wanted to address a couple of points:
* LINUX is less likely to be hit than Windows, but competition for boxes will make it a more popular target in the future. When Apple changed Mac OS to OS X they used FreeBSD (a close cousin to Linux) under the covers. As a result of the increased popularity we saw an increase in Mac viruses this year.
* If you aren't seeing things bounce off of your firewall from time to time, either your firewall isn't working or your ISP is blocking traffic for you. Knology stops many ports on behalf of its customers.
* If you use Linksys, Dlink, or some other devices that do wireless, you are most likely behind a hardware firewall. You can check this by staring a command prompt and then type 'ipconfig' and press ENTER. If your IP address is 192.168.x.x then you are behind a hardware firewall and your PC's firewall shouldn't be bouncing anything.
* Finally, PATCH PATCH PATCH... if you don't have Windows Update turned on then turn it on. Anti-virus programs can only kill software that has already attacked your computer. It also has to have been discovered by someone else (usually takes 12 hours or so before the updates are ready). By patching, you close the hole, and the attacks bounce off.