WordPress sites hacked twice in a week, days after upgrading WordPress

Hi everyone.

Are there any known security issues with the new version of WordPress? I have never been hacked before and I have just been done. This the second time in the same week and I don’t know whether its coincidental that it’s only a few days after I’ve upgraded to 3.5.1 or whether there are some vulnerabilities in it.

Both hacks have occurred in different places. The first one (on Tuesday) was just a case of over-writing the core index.php page with a not nice one, on all WordPress sites associated with my hosting account and a static HTML only website.

This second one, which happened an hour ago was a different. Replaced the index.php file in the main Themes folder in WP-content and the index.php file within WP-content. This one left comments leading to a hacking tool called GRITTY. looks like some sort of script to get certain information.

I’d gone through all the codex tools etc about my WordPress site being hacked but somehow they are getting in and I didn’t plan on spending my Saturday afternoon repairing websites! If anyone can give any help or advise that would be great.

Thanks in advance