The conduct amounted to a "serious lapse in judgment," the inspector general of the Homeland Security Department, John Roth, said in a statement accompanying an investigative memo he released.
"These agents, who were there to protect the president and the White House, were improperly diverted for an impermissible purpose."
The statement comes as Congress is investigating the Secret Service over a series of security breaches and scandals, including a recent incident where a man with a knife scaled the White House fence and dashed all the way into the East Room.
It found no legal justification for using Secret Service agents for such a purpose.
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"The Secret Service's mission is to protect the president of the United States, and not to involve itself in an employee's purely private dispute best handled by the local police," Roth said.
A Secret Service spokesman, Ed Donovan, said in a statement, "The Secret Service has received the OIG memorandum and is reviewing it for findings."
Compared to that failure and other incidents, including a prostitution scandal in Colombia, "Operation Moonlight" stands as a strange side note. It happened three years ago but came to light this past May in a report in The Washington Post.
A Secret Service employee who worked as the assistant to then-director Mark Sullivan was involved in a dispute with her neighbor, who was harassing her and assaulted her father. This "resulted in the loss of several of her father's teeth," the report says.