A database that contains the UK's 1.8 million postcodes along with other information such as longitude and latitude references has been posted on the web.
The information, which was updated as recently as July 8, is available on the Wikileaks site.
Wikileaks has not named the source of the database but it claims it is the Royal Mail's Postal Address File (PAF). However, the database on the web has considerably less locations and doesn't include names and full addresses like the PAF.
According to The Guardian, Royal Mail sells the PAF for a "considerable sum" and in 2007 made £1.6m from the database.
Royal Mail said it was investigating the issue.