Microsoft's UK website was defaced on July 6 by a hacker who goes by the pseudonym Apocalypse, according to information available at the web defacement archive, Zone-H.org.
The hacker managed to upload a picture bearing the legend "Free Rafa - hack is not a crime".
Rafa is a reference to the Venezuelan hacker Rafael Nunez-Aponte who was arrested three months ago in Miami, Florida.
Nunez-Aponte is suspected of being part of the "World of Hell" hacking crew, according to Zone-H.
Apocalypse is said to have been targeting US institutions and the US government ever since Nunez-Aponte was arrested.
According to the network services company, Netcraft, Microsoft's UK site is running Internet Information Server 5.0 on Windows 2000.