davorg is right. Computers (as they now exist) can never produce a truly random number. This is because, as Bruce Schneier puts it, "Computers are deterministic beasts: stuff goes in on one end, completely predictable operations occur inside, and different stuff comes out the other end." This enables back-computation.

Computers need humans to be truly random. They do this by having humans entropize their entropy pool with mouse movements, thus enabling the creation of Truly Random numbers.