I'm having some issues trying to understand my activity monitor on my macbook. It's actually technically a shared computer (although I use it 99% of the time), with about 4 different users who barely ever log on. It's for work, so I'm in an office building and using a cable for my internet. In the past two days, there have been two incidents where one of the user's names (who is rarely here and hasn't been on the computer in months), appeared on the activity monitor for about two minutes and then mysteriously disappeared. Any ideas? Why is this happening? He is definitely not logged in. Also there has been a message that another device on my network was using my IP address, but I figured that had to do with the fact that I am in an office building. Please advise! What's going on?