How can you "infiltrate" Wikipedia? It's a public website. It would be like infiltrating a shopping centre... If MI5 or any other organisation wishes to edit Wikipedia, they are free to, just like anyone else.
And, as usual the Slashdot summary is terrible. It says things were permanently removed from the database (sounds like oversight, which I don't think SlimVirgin has), when the article says nothing of the sort, it just says its been "surpressed" (reverted and protected as far as I can tell - since unprotected).