The most expensive computer virus of all time caused damage worth $38.5 billion! It was called “MyDoom” and was first spotted in January 2004. It became the fastest-spreading email worm ever.
Having a strong password can actually prevent most attacks. Facebook’s Chief Security Officer Alex Stamos is an expert and he has found that two factor authentication and strong passwords are simple solutions to protect yourself. ( Two factor authentication explained: Two-factor authentication: What you need to know (FAQ) How to make a strong password: http://goo.gl/Uhl3c5 )
Hackers are not necessarily criminals. White hat hackers test software for security vulnerabilities and try to get there before black hat hackers (Illegal Hackers) so that those security vulnerabilities can be patched.