The National Security Agency’s monitoring of Americans includes customer records from the three major phone networks as well as emails and Web searches, and the agency also has cataloged credit-card transactions, said people familiar with the agency’s activities.

The disclosure this week of an order by a secret U.S. court for Verizon Communications Inc.’s VZ +3.46% phone records set off the latest public discussion of the program. But people familiar with the NSA’s operations said the initiative also encompasses phone-call data from AT&T Inc. T +1.56% and Sprint Nextel Corp., S +1.94% records from Internet-service providers and purchase information from credit-card providers.