I only have two computers while three are shown.

In some cases, reinstalling your OS or running a cleaning app may force Mac Informer into thinking it's running on a new computer. Just click 'Delete this computer's software list' on your profile page (http://users.mac.informer.com/cpm_kouwenhoven/) for the two lists that look similar to each other, and then click Refresh in the client app on the corresponding machine.