There was an engineering director at one of my previous workplaces that was a little hard to reach. People though he was attending high level meetings including his reports. One of them called him once during work and he answered by the name of another company unintentionally. They spoke with HR and through some investigations found out the guy was coming to work and during the middle of the day going to his other job at a startup where he was the CTO. They fired him of course.