Editing the HOSTS file generates Event ID: 3004
When you edit the HOSTS file in Windows Vista, Windows Defender (real-time protection) will generate a warning in the Event Viewer about the change. This is normal as long as you really made the change/edit.
The default setting in Windows Defender do not pop-up any kind of message, it just write the above every time there is a change to the HOSTS file. You can also view a similar message from WD, open the program and click History