The Associated Press:

The Obama administration has been quietly advising local police not to disclose details about surveillance technology they are using to sweep up basic cellphone data from entire neighborhoods, The Associated Press has learned.

Citing security reasons, the U.S. has intervened in routine state public records cases and criminal trials regarding use of the technology. This has resulted in police departments withholding materials or heavily censoring documents in rare instances when they disclose any about the purchase and use of such powerful surveillance equipment.

One of the technologies police departments are being pushed to keep quiet about: Stingray. Here's how it works.