Crazy!

I found out this morning that someone stole my bank debit card number and made a bunch of crazy online charges to my account!  This has never happened to me before, and I'm feeling pretty violated at the moment.  I like to believe that most people out there are good, but there are some mean people runnin' loose out there.  :(  I'm glad my bank is being so helpful about it all...I'll have this worked out in just a few weeks I think. 

So how does this kind of thing happen?  What can I do to help prevent it from happening again?  Advice?  Thanks!!