Since few weeks on my WP blog I'm receiving a lot of spam. Some bots are "commenting" on my post doing advertising for things like: xanax, valium, tramadol, diazepam. I already get tens of such comments, so I decided that I have to do something. At the beginning I was looking for some WP plugin to solve the problem. The problem with most of them was that they were too complex (I'm a lazy person), or they just didn't work. In the end I've found that all the WordPress blog has already embedded such a feature. On the WP administration panel there is one option: Settings -> Discussions like bellow.
On the new page just scroll down and look for Comment Blacklist , you will notice a textarea input and here you can insert some keywords (one per line). When someone (person or boot) will add new comments if those keywords are present in the comment, the new comment will automatically be moved to Spam folder. So, I've added the keywords: xanax, valium, tramadol, diazepam; see bellow. In just couple of days, 97 comments were catch into the Spam folder :D.