We have recently opened the editing for anonymous users. As a consequence, we are spammed a lot more...
In the last days in particular, we have had in particular many spams from different IPs on a single page (but it is not so much of a problem because spambots are not capable of editing Wikidata pages, due to their different structure).
The website http://www.stopforumspam.com/ keeps an updated list of IPs that are spamming various websites, and all the IPs who spammed us on that day where already in their database. Therefore, it makes sense to use their data.
I knew the possibility to import Stopforumspam's IP list to the blacklist of a MediaWiki installation. However, it is stated that
[... you should] allocate a few more megabytes of APC cache... as, with this 1300000-byte file added to your configuration, you'll need it.
Since we already have problems with memory on the OmegaWiki server (only 1GB), it could have been problematic. An other problem is that the list is not refreshed automatically.
By clicking around, I then discovered the Check Spambots extension. This extension sends a query directly to some online IP-spam databases, among them Stopforumspam. An advantage is that you don't need more memory in your wiki, and the list stays up to date. An inconvenience is the additional time needed to query the external website (however, very quick from what I observed), but I made a small modification so that it does not affect logged-in users anyway.
Now we should have fewer spam, I hope :-)