We do have a shared folder on our workstations and I am hosting a shared printer. Could that be the cause?
Olhando para o Tipo de Logon no evento que você forneceu, é # 3 ...
Logon Type 3 – Network
Windows logs logon type 3 in most cases when you access a computer from elsewhere on the network. One of the most common sources of logon events with logon type 3 is connections to shared folders or printers. But other over-the-network logons are classed as logon type 3 as well such as most logons to IIS. (The exception is basic authentication which is explained in Logon Type 8 below.)