Think carefully before choosing your in-flight meal next time you plan a trip to the USA, because your choice could make the difference between receiving a welcome to America and being banned from boarding your flight.

As of last Monday, passengers crossing US borders are being assigned a secret risk-assessment score that cannot be seen or challenged, and which will be held on file for 40 years — a period judged by the US Department of Homeland Security (DHS) to “cover the potentially active lifespan of individuals associated with terrorism or other criminal activities”.

Secretary Michael Chertoff confirmed that once a passenger is on the blacklist, the agency transmits their name to the airline and “the airline is actually legally obliged to deny that person the opportunity to fly”.

Most worryingly, this score is not assigned by qualitative observation, but by a government computer program called the Automated Targeting System (ATS), which sifts through 39 items of intelligence provided by air and shipping lines for every inbound traveller to the States. This information, known as the Passenger Name Record (PNR), includes home and e-mail addresses, credit-card details, seat preferences and even in-flight meal choices from which the DHS claims its computers can identify terrorists and criminals.

Asked if this meant that a passenger ordering a halal meal on a flight to New York was potentially more dangerous than a vegetarian, the DHS replied that it “was not prepared to discuss security matters”, giving the same reply when asked if a preference for an aisle seat was more suspect than a window seat. ATS, it said, was “one of the most advanced targeting systems in the world”, without which the security of America’s borders would be “seriously impaired”.

In May, the European Court of Justice judged America’s demand for PNR data to be illegal, putting airlines in the tricky position of breaking US law by withholding information and falling foul of the EU by providing it. However, a new agreement was reached in October, with Europe agreeing to give the data freely so long as America agreed not to demand it.

The ATS system has angered human-rights campaigners on both sides of the pond. David Sobel, of civil-liberties group the Electronic Frontier Foundation, said the system broke America’s own Privacy Act of 1974, warning that it would “become an error-filled repository resulting in scores that will unfairly brand citizens as suspect for their entire lives”.

Liberty’s policy director, Gareth Crossman, said ATS was part of a worrying trend. “This is profiling rather than intelligence-led policing — there is a lack of human input, which is troubling.”

The DHS told The Sunday Times that passengers had nothing to fear. “In the unlikely event of an error, passengers can complain to our customer satisfaction unit,” it said.

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