How do we defend ourselves against patent trolls?

The patent system has a flaw within it's legal rights. Patent abusers called patent trolls, are able to obtain patents to which they're not entitled to. Then they use these patents in order to sue companies, mainly smaller companies who actually work in the field. They normally buy very vague patents, hoping that they'll be approved, or by buying vague patents. Then they use these patents in order to sue smaller companies who do not have enough needs to defend themselves, and they end up settling or sued. These troll companies do not produce anything so they cannot be countered sued. So what could small companies do to prevent this from happening? Or how could we change our laws to avoid these patent trolls?