In reply to Peter Knight (@peterrknight).

Thanks :)

I don't believe it's possible to block 100% of all automated spam-bots like this at all. If you can block it in an automated fashion without resorting to some sort of turing test, then it's going to be possible to bypass it in an automated fashion. You can block dumb bots, but there are always smarter bots and bot owners willing to throw more resources at the problem to get their spam through.