This is actually true--improvement on a design is not patent infringement, and you can file your own patent for an improvement of someone else's design. That h

This is actually true--improvement on a design is not patent infringement, and you can file your own patent for an improvement of someone else's design. That having been said, patent trolls don't really use patent infringement, but the threat of an infringement suit. They send threatening letters and wait for their target to realize that the court battle costs more than paying the fee.