The UK postcode database is reported to have been leaked online over at the Wikileaks site.
The database is said to contain all of the UK's 1.8m postcodes - as well as their exact geographical locations - data the Royal Mail jealously guards.
The data, in a plain text file, is described by Wikileaks as the "UK government database of all 1,841,177 postcodes together with precise geographic coordinates and other information", and is dated as last updated on 8 July 2009.
The Royal Mail, which made over £1.5 million from licensing the database back in 2007, is reported to have long resisted calls to make the information freely available.
A Royal Mail spokesperson told PC Pro that the company is "looking into it".