Kane Barratt was part of a gang who threatened victims during robberies
A convicted robber from Greater Manchester is being investigated after he was apparently able to update his Facebook page from his prison cell.
Kane Barratt, 21, from Stockport, is being held at Lancaster prison and is believed to have updated his webpage from a mobile phone.
The Ministry of Justice confirmed an investigation is taking place.
Paul Dillon, who had a knife held to his throat in an attack by Barratt, has criticised prison authorities.
The 55-year-old, an electrical engineer from Gatley in Cheshire, said he was "surprised and appalled" when he heard that Barratt had access to the social networking site.
"I don't think prison is tough enough and I don't think the prison authorities have been vigilant to have a mobile phone at your disposal while in prison and having your name on Facebook, like some urban legend.
"He was putting up messages like, 'The establishment have locked me up but my soul is still free'."
A Prison Service spokesman said prisoners would not usually have mobile phones or internet access.
Barratt, who uses the name Kane Reilly on Facebook, appears to have updated the site with photos and comments about life in prison.
Mark Leech said the government planned to block mobile phone signals in UK prisons
The Prison Service spokesman said: "Prisoners do not have access to mobile phones or the internet and cannot personally contribute to websites.
"This form of media is totally unregulated and we have no power to remove a social networking profile from the internet.
"Body Orifice Security Scanners will soon be introduced. These will be supported by high sensitivity metal detectors and mobile phone signal detectors.
"The Ministry of Justice has contacted Facebook in order to seek their help in assisting the Prison Service in preventing prisoners from making inappropriate postings on their website."
Barratt, of Heathland Terrace, is serving five-and-a-half years after admitting two robberies and three burglaries.
He was part of a gang that broke into a number of homes, terrorised victims and stole their car keys in a six-week crime spree in Bury, Oldham, Stockport and Rochdale.
Cars were stolen from victims, who were threatened with weapons such as machetes, and some homes were burgled more than three times by the gang.