"Our security system is fully impregnable"

From a c|net article on Internet taxes:

Sen. Ted Stevens, an Alaska Republican, said Wednesday that he'd like "to see an impregnable ban on taxes on the Internet."

As a wiser man than I has said, "You keep using that word. I do not think it means what you think it means."

UPDATE 20 June 2007. Although it didn't occur to me at the time, I should say that this remark is particularly surprising given Stevens's thorough grasp of the nature of the Internet(s).
UPDATE 11 PM 20 June 2007. Oh, dear. I was just reading a Roger Ebert review in which he describes the rules of the classic caper film, the first of which is that the film starts with an 'impregnable fortress'. Since I don't think of Roger Ebert as someone careless with his words, I went to check, and -- sure enough, 'impregnable' is exactly the word he wants, and there is no such word as 'unimpregnable' (which is what I would have used in that setting). This is quite embarrassing. Do I not even speak English? (Faithful remembers will remember that this is not even my first public linguistic cock-up.)