The Obama administration acknowledged the existence Thursday of a secret National Security Agency program dubbed Prism, which a senior administration official said targets only foreigners and was authorized under U.S. surveillance law.

The existence of Prism was first revealed Thursday by the Guardian and Washington Post, which reported the NSA has been tapping a direct vein of consumer data from Apple Inc., Google Inc., Facebook Inc., Microsoft Corp., Yahoo Inc. and other Internet companies, in some cases for years. The reports...