A computer with a series of numbers and the logo of the United States' National Security Agency is seen in this multiple exposure picture illustration. Reuters

The National Security Agency may have violated U.S. law for over a decade with the unauthorized surveillance of U.S. citizens' overseas communications, according to new reports on the agency's intelligence collection practices released by the NSA on Wednesday.

The U.S. spy agency released the highly confidential reports in response to a Freedom of Information Act lawsuit filed by the American Civil Liberties Union (ACLU). According to documents posted on the NSA website on Christmas Eve, the examples of violations include sending data on Americans to unauthorized recipients, storing such data on unprotected computers and retaining them after they were meant to be destroyed, according to Bloomberg.

“In general, each NSA report contains similar categories of information, including an overview of recent oversight activities… signals intelligence activities affecting certain protected categories; and descriptions of specific incidents which may have been unlawful or contrary to applicable policies,” NSA said, on its website.

The reports include a series of quarterly and annual accounts that have been made available to the president’s Intelligence Oversight Board, Bloomberg reported, adding that the reports cover the period between the fourth quarter of 2001 and the second quarter of 2013.

In one instance of an unauthorized surveillance practice, in 2012, an NSA analyst searched “a U.S. organization in a raw traffic database without formal authorization because the analyst incorrectly believed that he was authorized to query due to a potential threat,” according to the fourth-quarter report from 2012. The surveillance found nothing suspicious.

Another report revealed an incident, also in 2012, when an analyst “searched her spouse’s personal telephone directory without his knowledge to obtain names and telephone numbers for targeting.” According to the report, the analyst was advised “to cease her activities.”

The ACLU, which filed the lawsuit to access the NSA reports, claimed that the intelligence information collected by the spy agency was sometimes misused.

“The government conducts sweeping surveillance under this authority -- surveillance that increasingly puts Americans’ data in the hands of the NSA,” Patrick C. Toomey, staff attorney with the ACLU’s National Security Project, told Bloomberg in an e-mail. “Despite that fact, this spying is conducted almost entirely in secret and without legislative or judicial oversight.”

Meanwhile, the NSA said that it has multi-layered protections in place to ensure that no further errors occur in intelligence-gathering and retention.

“The vast majority of compliance incidents involve unintentional technical or human error. In the very few cases that involve the intentional misuse of a signals intelligence system, a thorough investigation is completed,” NSA said in an executive summary. “NSA goes to great lengths to ensure compliance with the Constitution, laws and regulations.”