It looks very suspicious to me like they are probing for vulnerable sites to hack with malicious intent. Sorry but I think my content is pretty innocuous!
Should my blogs suddenly go you will know the reason. If you suddenly get links to porn sites or sites offering you lots of money you'll know I have been "got at". I try to screen and delete dodgy comments that are clearly outright ads or with links to dodgy sites, but please let me know if you find any that I have missed.