my site has also been hacked at least 5 times - each time the mysql database has either been deleted or changed. i am using the latest wordpress and have repeatedly changed my user name and passord a number of times.
i reported the issue to my host (startlogic.com - they are quite big with over 80 000 customers) and this is what they say:
Your php application is leaving an open
door for hackers to enter the site
since some of your files are set
to the required 777 permissions.
You can try researching a more secure
blog application or one that does not
required permissions above 700.
appreciate any help as i really would like to keep wordpress but obviously need to secure it to prevent hacking