The Ping-Pong virus (also called Boot, Bouncing Ball, Bouncing Dot, Italian, Italian-A or VeraCruz) is a boot sector virus discovered on March 1, 1988, at the Politecnico di Torino (Turin Polytechnic University) in Italy.
The virus would become active if a disk access is made exactly on the half-hour and start to show a small "ball" bouncing around the screen in both text mode (the ASCII bullet character "•") and graphical mode.
No serious damage is incurred by the virus except on '286 machines (and also V20, '386 and '486), which would sometimes crash during the ball's appearance on the screen.
For this reason, users of machines at risk were advised to save their work and reboot, since this is the only way to temporarily get rid of the virus.
While the virus is active, one cannot replace the boot sector—it either prevents writing to it or it immediately re-infects it.