Just 12 hours after DayZ was released, it had over 88,000 copies sold, and within 24 hours it had a total of 172,500 copies. But one week down the track and we're looking at over 400,000 copies.
This is quite the achievement, considering it's still an Early Access build. DayZ has already seen a peak concurrent user base of over 40,000 players, which is another milestone in itself. Since it's release last month, there have been three major updates to the game, with many, many more to come.