WASHINGTON – Federal authorities are reviewing whether President Donald Trump's private Mar-a-Lago resort could be vulnerable to foreign spying, a person familiar with the matter said Wednesday.

Disclosure of that inquiry follows the arrest on Saturday of a Chinese national, who arrived at the Palm Beach, Florida, retreat the president has referred to as his Winter White House with two passports, four cellphones and a thumb drive that investigators said was infected with malware.

The criminal investigation involving the woman, Yujing Zhang, was continuing Wednesday. Federal authorities led by the FBI also launched an examination of potential intelligence vulnerabilities at Mar-a-Lago out of "an abundance of caution," as it was unclear what threat, if any, Zhang represented, said the person familiar with the probe, who was not authorized to comment publicly.

The FBI declined to comment.

Senate Democrats asked the bureau on Wednesday to assess Mar-a-Lago facilities and equipment Trump uses to access classified information while staying at his luxury country club.

"These potential vulnerabilities have serious national security implications,” Senate Minority Leader Charles Schumer of New York, Judiciary Committee ranking member Dianne Feinstein of California; and Intelligence committee vice chairman Mark Warner of Virginia wrote. They added that the Secret Service and White House Communications Agency were working together to establish several secure areas at Mar-a-Lago for handling classified information when the president travels there.

Trump was visiting Mar-a-Lago on the weekend Zhang was arrested, but he was not at the club when she arrived. He was 4 miles away at Trump International Golf Club in West Palm Beach. Some Trump family members, including First Lady Melania, were in Palm Beach Saturday, but it was not immediately clear whether they were at Mar-a-Lago at the time.

Trump is a frequent visitor to the resort, often accompanied by his family and top government officials.

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The intelligence investigation was first reported by The Miami Herald.

Trump said he was unconcerned about the possible security risk.

"No, I'm not concerned at all," Trump said at the White House, in response to a reporter's question. "We have very good control ... and it's getting better. Frankly, what we're doing with cyber is a story in itself. No, I think that it's a good situation.

"Secret Service is fantastic. These are fantastic people. And the end result, it was good. I think, probably, we'll see what happens – where she's (Zhang) from, who she is. But the result is they were able to get her and she's now suffering the consequences of whatever it is she had in mind. But I could not be happier with Secret Service."

How Zhang entered

At an initial Secret Service security checkpoint on the Mar-a-Lago complex, Zhang said she was going to the pool, and was allowed to enter after a Mar-a-Lago security manager said her last name matched that of a club member, an investigator wrote in a court filing.

When Zhang was asked whether she was a club member's daughter, she did not give a definitive answer, the documents state.

"Due to a potential language barrier issue, Mar-a-Lago believed her to be the relative of member Zhang and allowed her access onto the property," according to the documents.

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Zhang was "screened" at a Secret Service checkpoint before she was allowed to enter the club. She eventually made it to the club's main reception desk. Quizzed multiple times by a club receptionist the purpose of her visit, Zhang said she was attending a United Nations Chinese-American Association event later that evening–an event that did not exist, according to court documents.

“The Mar-a-Lago reception staff then determined that the individual should not have been authorized access by their staff, and Secret Service agents took immediate action resulting in the arrest of the individual,” the agency said in a statement.

After her arrest, an investigator wrote, she told Secret Service agents that a person she identified as "Charles" told her to travel from Shanghai to Palm Beach to speak to a member of Trump's family about the economic relationship between U.S. and China, the complaint states.

Zhang was ultimately charged with unlawfully entering a restricted building or grounds and making false statements to federal law enforcement agents. A detention hearing has been scheduled for April 8.

The Secret Service has said there is no system for keeping track of Mar-a-Lago guests, including those who speak to Trump.

Security concerns

Zhang's arrest came at a time when Chinese entrepreneurs in South Florida have launched consulting businesses offering to sell Chinese clients access to Trump and his family members at the Palm Beach resort.

For example, GY US Investments LLC's website claimed clients could “have the opportunity to interact with the president” and other “political figures."

That company is owned by Cindy Yang, who founded a chain of spas and massage parlors, including the Jupiter spa where prosecutors allege New England Patriots owner Robert Kraft solicited a prostitute. She sold the spa before the investigation that led to the charges against Kraft and others.

More: Founder of Florida spa tied to Robert Kraft case offered access to Trump and family at Mar-a-Lago to Chinese clients

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Yang frequently posted pictures from Mar-a-Lago on her personal Facebook account, including one with the president at a Super Bowl watch party at the resort. The New England Patriots won the Super Bowl that night.

A cached version of the website from the Internet Archive Wayback Machine, also shows Yang attending galas, dinners and political events, even getting an invite to the White House for one event.

House and Senate Democrats asked the Governmental Accountability Office to study Mar-a-Lago security after Trump discussed national security matters – in front of club guests – with Japanese Prime Minister Shinzo Abe in February 2017.

A club member posted pictures of Trump and Abe discussing a North Korean missile launch and looking at documents at a table on the dining terrace.