That annoying human spammers - Simple Solution for Spam in Drupal

Last couple of months we started to notice spam comments on our site. We have installed image captcha but obviously there are more and more human persons whose job is to manually spam sites.
We quickly created couple of triggers and actions that are sending emails and notify us when a new comment is created. Then we would manually check that comment and if it is a spam (>95% chance) we would put it into moderation.

Not a perfect process (and quite boring too) but it worked for us relatively OK. Spam gradually increased on our site - we started to get 2-3 human spam comments every day but we are always very busy with other projects... so we kept the non-perfect but working system.

Until one day we notice that we have about 20 spam comments that are laying around in our site and that were posted in the last month or so. Pfffft.... After quick investigation we figured out that our actions are disconnected from our triggers - who knows why, maybe some upgrade went wrong or somebody clicked in a bad place in a hurry...

We quickly reconnected actions and triggers but it was obvious to me that we should find a better solution. There are very advanced Drupal modules for spam out there like mollom... but they are all big and complex and I really wanted something dead simple.

So I started to investigate the situation and quickly figure the fundamental flaw of every spam - every spam needs to have at least one link that is leading to some spammer site. If somebody really wants to write a real comment on our blogs, he/she will maybe put some links inside, but a spammer will always put at least one link.

After 2h I had a module called spam_watchdog that is addressing this specific issue. This module will check newly added comments. If a link has been found in the comment, the module will put that comment in moderation and send a notification to site admin.

After 10 days of using it on our site we finally have perfect solution (or at least we have it for now ;) . spam_watchdog automatically moderates all comments with links. First 2-3 days of using we had 2-3 human spam comments per day. After that, they started to loose interest for our site (they are still trying, but there is nothing we can program against stubbornness ;-) . Now we have about one or two attempt of human spamming per week.

And this is exactly the solution I wanted to have: dead simple to install, just enable the module and forget about it. Combined with image captcha we eliminated the spam on our site (at least for now).

I am also attaching spam_watchdog module, maybe somebody else will find it useful.