ACLU finds Justice report on cellphone companies storing data for years

Many wireless carriers keep people's cellphone data for more than a year, according to a Justice Department document released by the American Civil Liberties Union.

The government document was meant to help law enforcement agents who were seeking cellphone records for their investigations. The ACLU obtained the document as part of a Freedom of Information Act request for records on how law enforcement agencies use cellphone data.

According to the 2010 document, the four national wireless carriers all keep records of which cellphone towers a phone uses for at least a year. This information could potentially be used to determine a person's location.

T-Mobile officially keeps the cell tower data for four to six months, but the document notes that the period is "really a year or more." AT&T keeps all cell tower records since July 2008, Verizon keeps the data for one rolling year and Sprint keeps the information for 18 to 24 months.

"Do you remember where you were on September 28, 2008? If you have AT&T/Cingular, your phone company may know. And they might tell the cops," the ACLU's Allie Bohm wrote in a blog post.

ACLU: Justice Dept. documentAll of the carriers keep details of phone calls for at least one year. For customers who pay a monthly bill (rather than buying pre-paid cards), AT&T keeps call details for five to seven years. T-Mobile keeps that information for five years.

The carriers also keep text message details for at least a year, but most of them do not retain the content of the message. Verizon does store text message content, but only for three to five days.