Category name changed by hacker – how …?

Hi.

My blog was recently hacked. Someone had managed to change the name of one of my categories to a meta redirect code, so that every page where the category name appeared was redirected to his site.

I have fixed the problem and upgraded to version 2.7, but I am curious as to how this was possible – how did the hacker manage to change the category name?

Any ideas? I would like to avoid future cases like this!