Word Verification

I have had to add word verification to my comments section because I have been plagued by one (it could be more than one) commentor who provides a link to a blog which, when opened, attempts to insert trojans and other malware into the visitor's computer. I've reported these links to Blogger.com, but have heard nothing back, so in the hope that these are computer generated comments which are triggered automatically by any new post, I've added word verification to try and block them. I'm afraid they're really getting on my nerves....

If I continue to received these comments despite word verification, I will try approving comments before they're shown. I'm just so worried that one of my visitors may click on one of these links and find themselves in trouble with viruses and goodness knows what else.