This is a virus detection. Viruses are programs that self-replicate recursively, meaning that infected systems spread the virus to other systems, which then propagate the virus further. While many viruses contain a destructive payload, it's quite common for viruses to do nothing more than spread from one system to another.
Indication of Infection
The above menu items disabled. On 30th day of any month, toolbar buttons are modified. The presence of the file C:\windows\Diablos.bas.
Methods of Infection
This virus is a direct infector. Opening a infected document will infect all workbooks already opened.