Other files describe the ultrasound detection system for protecting the perimeter fence and the runways, and detail the ID requirements for accessing every area of the airport.
A man found the memory stick in Ilbert Street, London W10, just 10 miles from Heathrow. Several days later, he took the device to his local library and studied the contents. When he realised the security implications, he approached the Sunday Mirror.
The unencrypted files may been hacked, then downloaded and transferred to the memory stick, which would raise very serious concerns about cyber security.
But given the location of the find, close to Heathrow, it is thought more likely that an airport worker had accessed the data and inadvertently lost the USB drive.
That raises two further possibilities. If a staff member or contractor had illicitly downloaded the files, it would again call into question security standards.
But it is believed more likely that whoever lost the memory stick had security clearance to access the data, if not necessarily to take the information away from Heathrow on a portable drive.
The airport has issued a statement about the discovery: “The UK and Heathrow have some of the most robust aviation security measures in the world and we remain vigilant to evolving threats by updating our procedures on a daily basis.
“We have reviewed all of our security plans and are confident that Heathrow remains secure. We have also launched an internal investigation to understand how this happened and are taking steps to prevent a similar occurrence in future.”
The discovery could trigger diplomatic tension between London and Washington about aviation security standards. This week airlines flying to America were instructed to impose tighter security rules because of fears at the Department of Homeland Security about another attack on US-bound jets.
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