Hacking, even Windows, is incredibly difficult. What is more likely is that you had trojans sucking information out (which were put there by you, they may be pretending to be something else, hence the name, but still put there by you), or fell to phishing sites.
Definitely read up on PC security!
Edit: I do remember an old episode of "The Screen Savers", in which they were trying to prove, once and for all, which OS was more secure (Windows or Mac OS, at the time it was Mac OS 9 I think), so they booted up a PC, and one of the brand new iMac G4s RIGHT after they came out (whatever the most expensive version was, the 15" 800Mhz I believe), the challenge was, the first person to place a text file on the desktop with their address, got the new iMac shipped to their house. Same went for the PC, which was a powerful custom build machine. They released the IP addresses on the air, and 10 minutes later, the PC had a new home. 72 hours later, when the challenge ended, the iMac had still not been touched.
There is something to be said about OSX security, but nothing compares to common sense, a basic understanding of computer security, and using discretion with everything you do on your computer.