My blog is getting lots of comment spam, something like hundreds a day !. I have been using spam karma 2 for quite sometimes, it does filter lots of comment spam for me until 2 weeks ago.
Since 2 weeks ago, my site became a target of multiple spam robots, it spam on my wordpress post from different IP address and with different signaturs and content. Various kind of content you can find from those spam. But you can easily see that those comments are generic type, it was written in such a way that it simply compliments your site but without anything in specific.
Those spam comments comes to me about once an hour from different IP address. Some how Spam karma 2 didn’t block nor flag those as spam. they all came into my comments awaiting approval.
Finally, I installed http://bestwebsoft.com/plugin/captcha-plugin/ , it asked simple math question to prove that users are Human instead of Robots!
This plugin is very easy to implement, no API key or what so ever, just install and activate it.