If you haven't looked into this, you'd be surprised what the USPTO finds "novel" and "non-trivial" enough to issue a patent. Cataclysm is over 100,000 lines of fairly dense C++ code, ample room to infringe some completely absurd software patent or another. Patents *are* impossible to guard against, which is why the DDA policy on them conforms to the industry standard, try and pretend they don't exist.
Most of my patent knowledge resides in EU and UK patent law but I believe patents in software in the US mainly revolves around "business methods" which aren't patentable in the UK and are in the grayish black area in EU. In fact the industry standard in pretending software patents don't exist is common because they are hard to grant and hard to test for infringement and hard to fight in court. I sincerely doubt you could find something which is infringing on a patent in DDA, you are more likely to find something infringing copyright and even then that can be arguable depending on if it's produced independently instead of being based on/copied on the original source.
Patents are pretty much dying worldwide with the only ones getting the big bucks being pharmaceutical and communications/electronics, no one cares about software or even general consumer goods with branding being much more important then patents.
If you can find something infringing any software patent that would be amazing to me
There needs to be a law skill in Cataclysm, probably once NPC's are fully integrated, it's the only way to ensure mankind's survival!