There's been a bit of a spate of template vandalism recently, and as a
result a discussion on the village pump over whether or not to
(semi)protect chunks of the template namespace by default - those with
views on the matter might want to drop by there.
Anyway, I wanted to mention a couple of helpful tools for dealing with
template vandalism when you find it.
a) If you look at the bottom of the edit page, there's a list of all
templates transcluded in the article, so you can open these and have a
look. It also mentions if they're protected or not - if not, and it's
widely used, this might be a good time to do so. [Obvious, I know, but
it took me a long time to notice them down there...]