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
If the day of the month is 5,10,15,20,25, or 30 a payload is activated that displays an unclosable message box:
The START BUTTON on the taskbar is grayed out and unclickable. However, the keyboard shortcuts (CTRL - ESC, or the WINDOWS key) still work. A registry key value is also modified that prevents WINDOWS from shutting down properly.
When attempting to shutdown Windows a message box is displayed:
Methods of Infection
This worm spreads via email, mass-mailing itself to users found in the Microsoft Outlook address book.
I-Worm.Urick (AVP), W32.Urick.A@mm (Symantec), WORM_URICK.A (Trend)