Patents are a valid protection against intellectual property theft. They are granted by the relevant authority on behalf of a sovereign state: for example, the US Patent Office in America, and the Patent Office in the UK. Once granted, patents assign exclusive rights to the assignee (inventor) for a limited period (usually twenty years) from the award of the patent.
This is a very strong protection of the inventor of a thing, as it prevents other, more established players from copying their ideas without licensing it. It is a valid and correct way of dealing with the protection of Ideas.
Unfortunately, over the last twenty years or so, the system has appeared to have begun falling apart and harming the very innovation that it was supposed to protect. Companies have sprung up that have a business model of buying up patents from dead companies and then suing other companies for infringements. Why do these people and companies chase these cases? Well, the rewards can be large for the victor and very damaging for the losing party.