I got fed up with it—77 in the last week so I have installed Akismet. It was quite easy really.
But I was still curious how they were getting through, even though I require registration and signin before commenting. I found the answer is this forum message by Otto42. It seems they are not comments but trackbacks so a panic turning off comments won’t stop it as some people have tried. In fact turning off trackbacks won’t work either because each individual old post will still have them enabled. The recommended answer is Akismet—done that, so let’s hope it works.
Wow! This is the size of the problem we are dealing with. Akismet is doing a grand job.