The Financial Services Authority is contacting 76,732 people to let them know they are targets for fraudsters trying to con money out of them.
Their names appeared on lists recovered from companies that the FSA believes were fraudulently selling investments in land or worthless, sometimes non-existent, shares.
Combined into one list, this is the largest number of intended fraud victims that the FSA has contacted in one go.
Most of the list contains the names and addresses of targets, but in 19,101 cases only email addresses are listed, so the FSA will be sending them an email warning.
The largest list was recovered from the premises of a firm that the FSA believes was operating an unauthorised business, but which cannot be named due to ongoing legal action.
All the lists are believed to be current and were being used to either sell fake or worthless shares, or plots of land with the promise of great investment returns once developed – even though this is unlikely ever to happen.