A new lawsuit claims that billions of people's records, including Social Security numbers, may have been stolen.The alleged breach occurred in April, and the hacker group USDoD perpetrated it, CBS News and Bloomberg Law reported. USDoD claimed to have stolen 2.9 billion people's records from National Public Data and then sold the information on the dark web.The stolen information allegedly includes Social Security numbers, full names, current and past addresses for the past three decades, and information about parents, siblings, and other relatives. What to do if your Social Security number was stolenIf your Social Security number has been stolen, the Social Security Administration cannot do anything if someone uses your information. The first step after finding out that your Social Security number was stolen is to go to the Federal Trade Commission's IdentityTheft.gov to file a personal recovery plan, which will include instructions on recovering your identity. You will also need to contact the Internal Revenue Service to prevent anyone from using your Social Security number to file a tax return or to get a job using your number. You should also contact the Social Security Administration if you believe the Social Security number has been stolen so the administration can help look at your statements.