The stock game doesn't account for stock splits. When a 2 for 1 stock split occurs, the game should double my shares. This means that if I buy 10 shares at $10 each, and the stock splits 2 for 1, then I should have 20 shares of $5 stock. The stock market cuts the price by the same split, so the total amount is the same, but the number and value has changed.
Since the game doesn't account for it, though, when a 2 for 1 split occurs, players lose half their value since the price is cut by 2, but the shares aren't doubled by the game.
This wouldn't be a problem, since it's a loss and players would then be responsible for selling stocks before a split, except in the case of a reverse split.
When a stock stays below $1 for too long, the exchange threatens to delist the stock. The company can combine shares to stay above $1 and thus stay listed. To stay listed the company might opt to do a reverse stock split, where you combine many shares into one share. So if you have a 1 for 10 split, then every 10 shares you have becomes 1 share. Like a regular split, the price is adjusted, so the price per share jumps up by 10.
This means that if I buy 200 $0.50 stocks ($100 value) and it does a reverse split of 1 for 10, then the next day when the market opens my shares are worth $5.00 each, but since the game doesn't split my stock, I still have 200 shares, and my value is now $1,000.
Since splits and reverse splits are often announced ahead of time, it's easy to game the system and increase one's total value by 5x and 10x per reverse split a few times a month.
You can obtain stock split information automatically via API and integrate it into the game. Please see
http://stackoverflow.com/questions/6119867/stocks-splitting-api-google-or-yahoo for one example.
This severely unbalances the game and makes it largely unplayable once players understand the loophole.
