At The Blaze:

In 2010 alone, Wired’s Threat Level explains, the government sent more than 24,000 National Security Letters to Internet service providers and other companies such as credit and financial institutions. Letters such as these come with a gag order in place, which requires the companies to stay mum on the fact that the government was seeking to acquire information on individuals.

Read the whole thing, keeping in mind that in other cases Google is very strict about not giving information to relatives trying to find out what’s happened to people who have disappeared.