tomda - 2:22 pm on Oct 24, 2008 (gmt 0)

If you have install the latest version of WP, then the security glitch is in one of the plugins you are using.

Usually, you go to log file to fetch information about your hacker or see any strange URL being called, etc...

Not sure that changing password regularly will help. Make sure all your plugins are up to date and do some search on the net for each of name "[plugin name] hack" to see if your plugins are vulnerable.