How do they make blog spam so hard to detect?

Anyone that has visited a blog or forum will have seen those vaguely annoying one line posts that are generally bad grammer and say nothing except what a great blog it is, how they’ll be back soon and to keep up the good work, right?

Well that is so-called ‘Comment Spam’ and it is the bane of website owners like email spam is to, well, just about everyone else!

What they’re doing is embedding a link to a website either in the profile of the user, the ‘sig’ in the post or even inline in the comment. The vain hope is that ubiquity = high search engine ranking. Anyone who owns a forum will tell you that 90% of their time is spent combing comments for trash like this. Services such as Akismet can catch an awful lot of spam, if supported.