A while ago I put in Panoramio a put a simple spam barrier in Panoramio. You want to post a comment? You have to tell me the name of your planet.
Stupid? yup, simple? yup, effective? until a couple of weeks ago, yup.
And then something happen. The spam barrier was somewhat broken, and big way. Panoramio was suddently flooded with spam. Either spammers around the world had got half the brain of an amoeba and were suddently able to reply with the name of their planet when asked, or some spammer had customized its boot to target Panoramio.
Or, well, none of these two options.
Taking a look at the database, it turns out these spam comments are not comments, they are trackbacks! Carefully crafted trackbacks to make them look as comments, mind you, but trackbacks none the less.
So if you have a wordpress site and have suddently be flooded with spam, even when you have a previously fine spam barrier in place, take a look at your trackbacks settings!