Marburg or Virus.Win9x.Marburg is a Windows virus that writes it's own code to the end of any infected file, so it will run the file followed by the payload.
When the executable is opened, it will appear to be a standard screensaver maze setup, fully working. However, this will now start an infection period for an hour, any file executed within this time period will expand in size, with the virus adding its code to the infected files. Nothing will happen for a further 6 months, where the core payload will trigger.
As long as the files are executed in the same hour as the infection, it will start drawing Critical Error icons across the screen once run. The computer is still fully usable, but again it may grow annoying.