A $10 billion-a-year effort to protect sensitive government data, from military secrets to Social Security numbers, is struggling to keep pace with an increasing number of cyberattacks and is unwittingly being undermined by federal employees and contractors.

Workers scattered across more than a dozen agencies, from the Defense and Education departments to the National Weather Service, are responsible for at least half of the federal cyberincidents reported each year since 2010, according to an Associated Press analysis of records.

They have clicked links in bogus phishing emails, opened malware-laden websites and been tricked by scammers into sharing information.

One was redirected to a hostile site after connecting to a video of tennis star Serena Williams. A few act intentionally, most famously former National Security Agency contractor Edward Snowden, who downloaded and leaked documents revealing the government’s collection of phone and email records.

Then there was the contract worker who lost equipment containing the confidential information of millions of Americans, including Robert Curtis, of Monument, Colorado.

“I was angry, because we as citizens trust the government to act on our behalf,” he said. Curtis, according to court records, was besieged by identity thieves after someone stole data tapes that the contractor left in a car, exposing the health records of about 5 million current and former Pentagon employees and their families.

At a time when intelligence officials say cybersecurity trumps terrorism as the No. 1 threat to the U.S. — and when breaches at businesses such as Home Depot and Target focus attention on data security — the federal government isn’t required to publicize its own data losses.

Last month, a breach of unclassified White House computers by hackers thought to be working for Russia was reported not by officials but The Washington Post. Congressional Republicans complained even they weren’t alerted to the hack.

To determine the extent of federal cyberincidents, the AP filed dozens of Freedom of Information Act requests, interviewed hackers, cybersecurity experts and government officials, and obtained documents describing digital cracks in the system.

That review shows that 40 years and more than $100 billion after the first federal data protection law was enacted, the government is struggling to close holes without the knowledge, staff or systems to outwit an ever-evolving foe.