The document reveals people from certain countries are always searched
The details of security procedures at US airports have been mistakenly posted online by the US Transportation Security Administration (TSA).
The document reveals which passengers are exempt from screening and that security can be reduced in peak hours.
Information which had been blacked out for security reasons was easily retrievable using ordinary software.
The TSA said there was no threat to security as the document was outdated, but that it took the issue seriously.
The document was posted on the TSA's Federal Business Opportunity site in March, said the Associated Press news agency.
Its existence was reported in a blog, the Wandering Aramean, on Sunday, which pointed out that the blacked-out sections could easily be read.
Those sections cover information about which passengers should always be selected for extra screening unless specifically exempted, including people with passports from Cuba, Iran, North Korea, Syria, Somalia and other countries.
The document says that prosthetic devices, medical dressings, wheelchairs, scooters and surgical footwear may be exempt from screening for explosives at certain times.
It also says that at busy travel periods, screening procedures may at times be reduced to 25% of normal levels and that properly accredited flight crew are not subject to restrictions on carrying liquids and gels on to aircraft.
Clark Kent Ervin, former inspector general of the Department of Homeland Security, told ABC news the document was "an appalling and astounding breach of security that terrorists could easily exploit".
But the TSA said that while it was taking the matter seriously the document itself was outdated and the public was not in danger.
In a statement, it said it had "many layers of security" to protect the public and had "appropriate measures in place to effectively screen passengers at airport security checkpoints nationwide".