Amazon.com investors drove shares down sharply on Thursday due to weakness in the retailer's cloud computing unit and lower-than-expected forecasts for first-quarter revenue and profit.Amazon's shares fell as much as 5% in extended trade after the fourth-quarter earnings report,

Amazon's beat Wall Street's overall expectations with $187.8 billion in net sales, up 10%, and came in well ahead on the bottom line, with earnings of $1.86 per share, vs. expectations of $1.48 for the fourth quarter.

Wall Street’s expectations on fourth-quarter earnings and revenue today, but sales in its all-important cloud computing business came up short, and guidance for the current quarter was light. As a result,