I finally found a good WordPress anti-spam plugin that is free and does not get affected by caching plugins. Try to look for anti-spam plugins int he WordPress admin console and the first few results given to you are not really free.
Sure, they list it as free but once you start using it, it gets problematic and they do not really work flawlessly. Later on, you will find out that the free version is actually crap and you need to buy the license in order to get the plugin working.
Antispam Bee however, is TOTALLY free and straightforward. Just add, install and activate. That’s it!
The plugin itself has quite a number of options to make it flexible according to your choosing. However, if you want to go for the default settings, they still work the way you want it to: block unnecessary comments.
Even if you are using caching plugins it won’t get affected.
Easy and extremely productive spam-fighting plugin with many sophisticated solutions. Try it!