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 virus will display the above message on the 13th of the month.
Methods of Infection
Opening infected documents will directly infect the local Word environment and any document used thereafter.