Comments spam

[alexis]

Hi there
I have been hit by some kind of "robot" that insists on leaving spam-like comments on my website - there are hundreds of them every night and I spend every morning clearing them - I have now disabled comments but I like that feature a lot so any advice on how I can fight this would be welcome.
BTW all the comments left have email addresses of the type hello@hello.com or think@think.com etc - obviously these are auto-generated.

thanx
Alexis