Attacker changed my login credentials

I came in this morning, and tried to login to my site. After several attempts, I could not.

When I checked my DB, I noticed that the attacker had changed my username and password – or rather, taken over my username, changed my password, and reduced me to a subscriber.

Anyone else who has experienced this scenario? What can be done about it?

Attention: hackers are on the prowl. And the guys via the link below have hacked me twice:
[Link removed]