"to ensure they were "not shady characters""

"A National Security Agency employee was able to secretly intercept the phone calls of nine foreign women for six years without ever being detected by his managers, the agency's internal watchdog has revealed."

The unauthorised abuse of the NSA's surveillance tools only came to light after one of the women, who happened to be a US government employee, told a colleague that she suspected the man – with whom she was having a sexual relationship – was listening to her calls.

The case is among 12 documented in a letter from the NSA's inspector general to a leading member of Congress, who asked for a breakdown of cases in which the agency's powerful surveillance apparatus was deliberately abused by staff.

The letter, from Dr George Ellard, only lists cases that were investigated and later "substantiated" by his office. But it raises the possibility that there are many more cases that go undetected. 

The Atlantic lists those twelve incidents.
1. In 2011, an employee facing a polygraph test confessed to performing a SIGNIT query "out of curiosity" on the home phone number of his girlfriend, who was a foreign national. He was able to view metadata from the query. The employee wasn't disciplined, and retired in 2012.

2. Another employee confession before a polygraph test: this time, in 2005, the employee admitted that he had a SIGNIT collection run for a month in 2003 on his girlfriend's number in order to figure out whether she was up to anything that "might get [him] in trouble." His violation was referred upwards, but he also retired before disciplinary action was taken.

3. In 2004, and employee collected voice recording of her husband on a foreign telephone number that was unfamiliar to her in her husband's phone, because she suspected he was being unfaithful. She resigned before she was disciplined — though the letter notes that the recommended disciplinary action was to fire her.

4. Between the years 1998 and 2003, one employee of the agency listened to the calls of nine female foreign nationals. That collection resulted in the collection of voice data on two U.S. citizens. It was discovered when a foreign national employed by the U.S. and "having sexual relations" with the employee in question suspected something was up, and told another employee of the agency that she thought the employee in question was listening to her phone calls. He resigned before he was disciplined, while suspended without pay.

5. Another employee targeting female foreign nationals. This time, it was between the years 2001 and 2003, and the employee resigned before being disciplined.

6. An employee, under a polygraph test, admitted to accessing communications of two foreign nationals without authorization in an investigation completed in 2006. He was suspended without pay for 10 days, and prohibited from getting promotions or other awards and pay increases, for a year.

7. In 2011, a female employee assigned and then reviewed data collection on her boyfriend's telephone number. She also routinely ran foreign numbers she collected from social situations through the system to make sure her new acquaintances weren't "shady." She resigned before being disciplined.

8. On his first day with access to SIGNIT in 2005, a military employee ran six email addresses of his former girlfriend through the system, just to "practice" using it. In the investigation, he testified that he hadn't read the content of those queries. He received a demotion in rank, and in pay, and was denied a security clearance because of the incident.

9. In addition to querying his own name, this employee repeatedly ran his girlfriend's number through the system in 2006, along with her name. He also queried another number without authorization two times. It was recommended that he be fired, but he resigned before that happened.

10. In 2008, an employee looked up information on two relatives of a "valid intelligence target," who where in the U.S. The employee received a written reprimand.

11. A military member of a tactical intelligence unit used the SIGNIT system to query the communications of his wife in 2009. She, also in the military, was stationed abroad. The abuse was discovered in an audit. Eventually, the matter was referred to the DOJ in 2009, after the person in question suffered a rank reduction, pay reduction, and revocation of access to classified information.

12.  A military member repeatedly queried foreign telephone numbers, apparently in order to learn foreign languages. The abuse was discovered in an audit and he was barred from accessing classified information.