As I related before (in my Wandering Bob story), I was in the engineering group at a "widget" factory. At one point the place had three shifts and was busy as anything so the company hired in a bunch of minimum wage temporary workers. While some people had worked at the company for years, even decades, suddenly there was an influx of new faces also a huge turnover with the temporary workers since their assignments usually were not the greatest.
One day the engineering and prototype departments had the female HR assistant come to us to ask if we had a worker named "John Smith" doing special prototype production assembly or other special fabrication helper duties for our departments. We had never heard of him.
Our prototype shop supervisor got the real story later by hanging around the HR department when the manager was out. It turned out that "John Smith" was a temporary worker on third shift (graveyard 11pm to 7am) and had been working there three months but best they could figure out was that after the first month he only showed up to punch in and to punch out. Problem was that he stopped being on time to punch out the last month so he went over his 8 hour day and started to get overtime! The overtime triggered HR to ask questions about where he was working the overtime in order to bill the hours to the correct department or manufacturing area. Oops, they found out he wasn't working at all...
He became our department hero for a couple of weeks...