The person/company with the patent hasn't contacted me. A few years ago they said they wanted to build a business around my solution, which I thought was cool. But they certainly didn't claim a patent.
Do I need to do anything as long as they don't come after me?
1. What was the file date the patent got? 2. Is that file date after any date that you can prove that you had invented the system (best if it was publicly available already). 3. What country was the patent filed in?
Now, worst case scenario, the patent is prior to any date where you can prove that you invented the process (or whatever the patent is covering), and the patent was granted in a country in which you operate.
Under those circumstances, what does the patent holder want, and how much damage are they willing to do to get it. What are your options?
Annoying case 1 - the patent was granted prior to the date you can prove you invented it, but was granted in a country you don't operate in and don't care about.
they can't really do anything unless they can get the patent granted in a region you do care about. It's now up to you to ensure that doesn't happen.
Annoying case 2 - the patent was granted in a region you sell in but the date granted was after a date you can prove prior art.
You may have to prove prior art and go through the process of getting their patent nullified. If you're working with consumer software, I probably wouldn't worry about contacting your customers. But if you are B2B and are close with your customers, get some 3rd party advice on if you should let them know of the situation, in the event that the patent holder may start contacting your customers. I'm not sure of the right move there.
That's my 2 cents, but definitely get input from an expert.