The game is played on a 8 x 8 grid, drawn on a piece of paper. One player 'O' has a blue pen, and the other 'X' has a red pen.

The game starts with an 'O' virus in the bottom left corner, and an 'X' virus in the top right corner:

'O' plays first and has one move, to balance out the advantage of starting. The players then take turns in making three moves in a row.

Each move can be to:

• Create a new virus, by writing their symbol in accessible empty cell, or
• Kill one of their opponent's viruses in an accessible cell, by shading over the opponent's symbol.

A cell is accessible if it is:

• Next to one of the player's live viruses, horizontally, vertically, or diagonally, or
• Connected to one of their live viruses through a chain of their opponent's killed viruses.

For example, in the following opening 'O' played at B2, 'X' created three new viruses, and 'O' created two and killed one of 'X's:

A player must make all three moves, and if they can't move their opponent is the winner.