Tobias Schlitt has posted this new item over on his blog today with a bit more information on the PEAR Services_Trackback library and his effort to create the method to keep comment spam away.

A few weeks ago I announced the release of Services_Trackback 0.5.0, which has a new module system for integrating spam protections into your trackback mechanisms. While the most easy filter (the bad word list) worked quite well for the first time frame, but as usual it did not take long for the spammers to work around that with using entitie encoding. Of course to get around that from the anti spam point of view is very simple, too, with simply reconverting that stuff before running the bad word check. But that's not really the sense, because the spam fraction will not need long to come around this, too.

So, basically what I'm currently thinking about is, how to build a (to some degree) reliable spam protection.

He goes on, discussing some of the other options for blocking spam (blacklists, greylists, vertification of the sender) that the package doesn't support yet. He's also looking for opinions as to other methods to include in the library for the future as well...