I got hacked as well 2 weeks ago for 20m. My computer is pretty secure (or atleast that's what I thought :P) but there are a lot of ways you can get hacked. Keyloggers, Rats, Rootkits, Phishing sites, and so on.. If he's a good hacker your virus scan won't pick it up, so yeh.. You should be very paranoid about what websites you visit (yes even visiting certain websites will get you infected) and what files you download. Youtube videos are a very popular method of spreading keyloggers / trojans / malware nowadays so don't download anything from youtube (links in description). Usually there are a lot of comments from dodgy people saying "thank you" etc.. but that does not make it any more credible.
I'm pretty sure I got hacked by a dude on Advertising other bots isn't allowed.. My little brother wanted me to buy a script for him since I did not have time to create one for him. The day after I ran that script I was hacked. He used a devloader so I couldn't see the source, so yeah. Don't trust anyone :P.
And use bank pin etc.. Good luck starting up again.