AnswerIP Addresses are shown when a machine starts activities like AV updates. These connections will not be authenticated by GFI Web Monitor.
Computer accounts ($computername) are displayed when a service is trying to access an application. The activity will happen before the user gets authenticated and will be registered under the computer account instead.
These requests can be blocked by a GFI WebMonitor policy such as the Malicious policy. In these cases the connection will be dropped before the user attempts to authenticate.