Hackers infiltrated the Department of Energy’s computer system over 150 times between 2010 and 2014, according to federal documents obtained by USA Today.

The records — received through a Freedom of Information Act request — reveal a blanket of digital attacks the agency has been struggling to thwart for years. In total, hackers targeted DOE networks 1,131 times over the four-year span, successfully cracking the network 159 times.

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As the department overseeing the country’s power grid and nuclear weapons stockpile, the Energy Department is an attractive target for overseas cyber spies.

Researchers believe hackers from Russia, China and Iran have all been probing the U.S. power grid for several years, mapping it out and seeking vulnerabilities.

It’s not clear whether the DOE hackers picked up any sensitive data about the country’s power grid or nuclear stockpile security during their intrusions.

"DOE does not comment on ongoing investigations or possible attributions of malicious activity," department spokesman Andrew Gumbiner told USA Today in a statement.

But records show the assaults did hit some of the agency’s most sensitive systems.

The National Nuclear Security Administration, a sub-agency within DOE that secures the country’s nuclear weapons, was hit with 19 successful cyberattacks over the four years.

Like nearly every government agency, DOE has been scrambling to bolster its cyber defenses in recent years.

In a 2013 oversight report, the agency’s inspector general noted “unclear lines of responsibility” regarding cybersecurity and a “lack of awareness by responsible officials.”

Senate Democrats have been warning that without boosting the agency’s funding, the electric grid will also remain vulnerable.

“The reality is that this is a system that is not as well protected as it should be,” Sen. Martin Heinrich Martin Trevor HeinrichSenate Democrats demand White House fire controversial head of public lands agency Senate Democrats seek removal of controversial public lands head after nomination withdrawal Five takeaways from final Senate Intel Russia report MORE (D-N.M.) told reporters in a July conference call. “This is a grid that evolved over 100 years and much of it is based on fairly simple technology.”

Democrats and Republicans are currently battling over an Energy and Water Development funding bill, which Heinrich and some of his Democratic colleagues believe handcuffs the agency in its efforts to protect itself and the power grid.

The GOP has pushed back.

After the bill cleared committee in May, Sen. Thad Cochran William (Thad) Thad CochranEspy wins Mississippi Senate Democratic primary Bottom Line Mike Espy announces Mississippi Senate bid MORE (R-Miss.), who chairs the Appropriations panel, called the bill “forward-looking” on energy security, “despite limited resources.”