Facebook is, for most of us, a rather harmless, if addictive, pastime. It is tremendous fun to post whacky status updates, "poke" friends, "Like" pages and share photographs videos and all the generally random conversations that make up significant portions of our daily lives.

There are, however, darker sides to the popular social networking Web site.

According to the Mirror, the UK's Ministry of Justice has confirmed that nearly 350 violent prisoners were caught using Facebook (posting status updates), while serving sentences that expressly forbade any such pleasures. The prisoners were, apparently, using the networking service to taunt the victims and families of their crimes, from behind bars.

The information came to light when a Freedom of Information request was answered. It also raises serious questions about the security arrangements in UK prisons.

A Daily Telegraph report from Australia even suggested that some other inmates may well have been running entire criminal organisations through the networking Web site.

Facebook has been quick to react to these statements and has reportedly shut the particular profiles down.

Furthermore, in response to these reports, a spokesperson for the Prison Service was quoted in the Mirror's report: "If a prisoner is found in illicit possession of a mobile phone or other contraband they will be dealt with appropriately by the prison."

It further appears that the prisoners in question worked around the limited access they were given to the Internet by posting using smartphones that were smuggled into the prison.

"These perpetrators should not be able to have access to mobile phones in prison," Jean Taylor, from Families fighting for Justice, stated, as reported by The Telegraph.