AT&T said it fired an employee Monday, for inappropriately gaining access to thousands of customers' data and has promised to reverse any unauthorized charges.

AT&T, the second largest wireless carrier in the U.S., reported a security breach involving 1,600 customers by a company employee in August. The carrier is sending a letter to all affected customers explaining the incident and the course of action.

The company noted the security breach by its employee resulted in an immediate termination. According to AT&T's letter to its customers published on the website of the Attorney General of Vermont last week, the security breach may have compromised customers' Social Security numbers, driver's license numbers and the subscribed services at AT&T.

AT&T is also compensating the customers affected by the breach with a free year of credit monitoring services and access to the credit report. Any unauthorized charges on the customers' accounts will be reversed. AT&T said the incident has been reported to the federal authorities for further investigation.

"We take our customers' privacy very seriously and value the trust they have in us," Mark Siegel, an AT&T spokesman, said in a statement, New York Times reported. "Unfortunately, we recently learned that one of our employees did not follow our strict privacy rules and inappropriately obtained some customer information. This individual no longer works at AT&T and we are directly contacting the limited number of affected customers."

AT&T strongly recommends setting up a passcode for the security of the account, which will be used to verify a user over the phone or in retail stores. It will also be handy while signing into the online accounts. If subscribers already have a passcode, the carrier suggests users to change it online or by calling the customer service.

AT&T's incident adds to the pile of growing hacking attacks on companies like Home Depot, Target and some high-profile cases like the theft of celebrity photos from Apple's iCloud service in August.