In addition to marking the end of 2015, December marked what the Office of Personnel Management surely hopes is the end of the repercussions of a massive cyber security breach earlier this year.

The office recently mailed the last of the notices that were sent to more than 21 million people affected by the breach of government security clearance files, according to an article in The Washington Post.

About 1.5 million of those signed up for identity and credit monitoring services.

The breach “involved personal and career information on 4.2 million current and former federal employees,” the Washington Post article states. The others were people who applied for or renewed their security clearance, primarily since about 2000.

Besides showing a vulnerability in the Office of Personnel Management’s record keeping effort, the breach exposed the personal information of those affected, including fingerprints, sexual histories and past financial or legal problems.

The cleanup and precautions taken following the breach have revealed another curiosity: Some people who have received notice that their information was compromised never have held security clearance, nor have they ever worked for the federal government. Instead, their social security numbers likely were used to perform some sort of lesser background check, according to a different article in The Washington Post.

These victims include more than 1,100 WPS Health Solutions workers in Wisconsin.

Also included are thousands of reporters, photographers and cameramen from across the country who had credentials to cover federal agencies such as the Defense Department, the White House and the CIA, according to Independent Women’s Forum.

If your information was involved in the breach, we recommend that you sign up for the credit monitoring service being offered by the government. You can find more information about that service at the Office of Personnel Management website.

“We are hopeful that going forward, systems are in place to better protect the personal information of those who have applied for clearance,” says Catie Young, a security clearance attorney.