what’s the best way to answer a recruiter/employer asking about how much you make with your current/last employer?

If I answer the question truthfully, they'll use it to lowball me. I'm not sure if I should lie and say I make what the best paid coworker in a similar position makes where I am now. I'm unsure they can find about it. I'm unsure about answering this: 'I'm not going to answer that question because it doesn't affect the job you are offering'. I'm afraid this might backfire, depending on how think skinned the employer/recruiter is.