Can u avoid getting hacked?

I have been hacked twice now. Is there any actual way from being hacked? I have lots of good stuff and when a hacker sees the stuff they hack my acct and delete my characters. I called the Blizzard tech support line and they told me to mix numbers with my password. So i did and hey guess what? I got hacked 3 weeks later! So can anyone tell me how NOT to get hacked?

thx,
-Spector-