version .11 was released way last year and then .12 was some time later , .13 has been out for over a month.
no software is immune to hackers, and once one of them finds a hole, they all go crazy like a shark attack,(no offense Mr. Sharkey )
anyway, this latest hack does make changes to your database, so just upgrading to the new version now, will not solve the immediate problem,
you should go into the database, look for the theme table, find the offending theme , make note of the ID# , and delete it.
then, browse the users table and check to see if all your members are using that theme ID#, of so you will have to change something. what I did was choose a different style and change it's ID# to the same ID# that the bad theme was using.
hope this helps,