>I just got an offer for a job, but the background check is still in progress.
>How can they make an offer before the background check is complete?
>
>Background check is being done by a third party.
>Has anyone else been through this?

It's quite common.

In most instances, the offer letter states that the offer is contingent on successful background check.

I can't speak for all situations, but in many cases they simply want to verify that any critical information you provided them is accurate.

Just hypothetically, if you had been convicted of a crime but stated otherwise on an application, they could rescind the offer if a background check demonstrated that you weren't truthful.

Now, in scenarios where you'd have certain positions in a financial institution, they could conceivable do a credit/financial check. The theory is that anyone deeply in debt might pose a risk as an employee. I'm not saying it's right, but it can happen (though probably unlikely for an I.T. person)

If you were truthful with the company during the interview process, I wouldn't sweat it too much. Normally background checks don't take very long.