Stock index futures slid further on Friday as Wachovia Corp, the fourth-largest U.S. bank, disclosed exposure to securities linked to subprime mortgages, heightening investor concern about the impact of the credit crisis.

S&P 500 futures fell 12.5 points and were below fair value, a formula to evaluate pricing taking into account interest rates, dividends and time to expiration on the contract.

Dow Jones industrial average futures dropped 88 points, and Nasdaq 100 futures slid 13.5 points.

(Reporting by Ellis Mnyandu; Editing by Kenneth Barry)