Now, records show how far beyond Silicon Valley the practice extends — encompassing scores of banks, credit agencies, cellphone carriers and even universities.

The demands can scoop up a variety of information, including usernames, locations, IP addresses and records of purchases. They don’t require a judge’s approval and usually come with a gag order, leaving them shrouded in secrecy. Fewer than 20 entities, most of them tech companies, have ever revealed that they’ve received the subpoenas, known as national security letters.