France has flagged more than 78,000 people as security threats in a database intended to let European police share information on the continent's most dangerous residents.
The total is more than all other European countries put together, according to an analysis by the Associated Press.
The data has led to questions about whether the system is being misused, with different countries applying different criteria.
A German parliamentarian, Andrej Hunko, raised the alarm about the European database in a question to his country's interior ministry.
In 2017, more than 134,000 people were flagged for the secret international checks on people considered security threats.
To put the French number in perspective, the country's intelligence chief said late last year that 4,000 suspected extremists were being monitored as highly dangerous.
"The increase in alerts cannot be explained by the threat of Islamist terrorism alone. Europol reports a four-digit number of confirmed foreign fighters, yet the increase of SIS alerts in 2017 is several times that," Mr Hunko said in a statement late last month when he released the interior ministry response to his query.
That response included a spreadsheet detailing for the first time how many discreet checks each European country had flagged up last year - more than 134,000 in all.
"This could mean that families and contacts of these individuals are also being secretly monitored. It is also possible that the measure is being used on a large scale for combating other criminal activity," Mr Hunko said.
The number of French police entries "indicates a misuse" of the system intended to monitor dangerous criminals, he added.
The Schengen database - which is separate to the Europol database and far more widely used - forms the backbone of European security, allowing police, judicial authorities and other law enforcement to immediately check whether a person is wanted or missing, or a car is stolen, or a firearm is legal, for example.
The database was checked five billion times in 2017 alone, according to the director of the EU-LISA agency, Krum Garkov.