Shares of the Marlboro maker may have more room to fall before they hit deep-value territory.Take one quick look at the stock on a screener, and you may think "undervalued" is an apt description for Altria Group (MO +0.60%).The company, which sells Marlboro cigarettes in the United States, has a low forward price-to-earnings ratio (P/E) and a high forward dividend yield and looks very cheap today. But don't underestimate how much "cheaper" shares could get in the months ahead.NYSE : MOAltria GroupToday's Ch ...