You cant own knowledge, but you can patent software. Tens of thousands of software patents are issued every year, and patents—unlike copyrights—cant be evaded by "clean room" programming. If the idea is patented, the patent holder owns it even if you "invented" the same thing with no knowledge of that prior work.
The threat of finding that someone else, in effect, owns the product that you spent years developing is a major opportunity for intellectual property law firms like the one that posts a sign at San Jose International Airport.
Just as a product team takes the trouble to search for trademarks and URLs that arent already taken, a patent counsel is quickly becoming an indispensable part of any commercial software launch.