This is not Thesis specific, but it's important enough to go off topic about
:
Be sure and update to the latest Wordpress version (currently 2.5.1) and update all your plugins as soon as possible, too. The
Wordpress Automatic Upgrade Plugin makes it nearly painless to upgrade.
There are some really nasty exploits of security holes going on out there.
I got hit with a spam injection attack last week, which inserted hidden links into my footer. Even though it was only up for about 4 hours, my Google traffic has tanked. Others have been hit with far nastier stuff this month, and at least one person I know had to rebuild their database.
Old versions of Askimet have issues and need to be upgraded too, and reportedly the popular wp-contact plugin has vulnerabilities as well. ( I haven't yet seen a fix for wp-contact, so I've disabled it for now)
So while you're tweaking your theme, don't forget to update Wordpress itself!