The BBC claims that home addresses and personal email details of all 38,000 runners who took part in Sunday's race were accessible to anybody heading to the official race website throughout Monday. The details were freely available on the section of the site which allowed people to order commemorative medals with inscribed race times.
Shadow chancellor Ed Balls, singer Will Young, chefs Gordon Ramsay and Michel Roux Jr, BBC newsreader Sophie Raworth, Olympic gold medallist James Cracknell and several cast members of Coronation Street and The Only Way is Essex were among the high-profile runners.
Organisers have apologised and said that the glitch has now been rectified, but the details were available for several hours.
The problem apparently came to light when a member of the public emailed a BBC television presenter, who contacted race organisers.
"We apologise for this error, and are grateful to the BBC for bringing it to our attention," said Nick Bitel, the chief executive of the London Marathon.
"We immediately made sure that the glitch was corrected.
"We do not believe that this has led to a substantial number of individuals' details being accessed by members of the public."