Manchester United have begun legal porceedings against a supporter who leaked the contact details of 400 of the club's corporate clients on the internet, leading to property being damaged and people being visited at their home addresses.
The club say they had no option but to take out a writ against Thomas McKenna, of Greater Manchester, who had posted the information on a website set up in opposition to the Glazers' ownership of the club.
In the writ filed at the High Court, United state that the information was stolen from them - though it is not alleged that McKenna himself took it - and it must either be destroyed or returned to the club.
United are also seeking a court injunction to prevent any repetition, and also claiming damages.
A United spokesman said: "The theft of data led to some of the companies named on the list having their property attacked and suffering significant personal distress.
"The club has a duty to demonstrate to all our fans that we will not tolerate that and will take action against the perpetrators. We take data security very seriously. Doing nothing was not an option.''
It is believed United have no record of McKenna as being a season ticket holder or part of any membership scheme.