A leading cyber-security company is warning people travelling to the US that American authorities might search their social media posts before they depart.
C3IA Solutions, based in Poole, Dorset, said that to get a visa, applicants must complete the US Electronic System for Travel Authorisation (ESTA).
When they do so, they must provide the names of their online accounts for the last five years.
It allows the US authorities to check photographs, locations, dates of birth and other metadata.
It details information including the latitude and longitude of the locations of photographs as well as the date and time.
And in future the authorities might also request passwords – something that has previously been considered.
Matt Horan, security director of the leading cyber-security firm, said: “Many people are unaware of the level of the checks and naturally some find it quite intrusive.
“Ostensibly this is about screening out terrorists and individuals that may have had contact with ‘special interest’ groups.
“This stems from the President’s executive order in March 2017 that put ‘extreme vetting’ into place.
“It is highly controversial and its effectiveness has been questioned, but nevertheless it exists, and if you want to enter the US for business or pleasure it is a necessary evil.
“And if it is discovered that people haven’t disclosed the details required then visas might not be forthcoming, or worse still you may get to the US customs and be turned back.
“It is always wise to assume any social media posts, no matter how far back in time – and indeed those in private groups – could become publicly available for all to see.
“And remember that the US authorities might not understand the humour, innuendo or sarcasm of a Briton.
“In future the State Department might request passwords as well, and this really will focus minds.
“Our online footprint is something about which there is lots of debate and from a security point of view it is a potential weakness and we urge people to be careful and cautious when using social media.
“We have seen many people in the public eye being caught up in a media storm because of an old or poorly phrased tweet or post.
“But it is not just famous people for whom this sort of thing is a potential problem; anyone can be affected and it might prevent them being able to travel to the US.”