"Lord" Hugh Rodley, 61, who bought his title, was convicted of conspiracy charges dating back to 2004. Soho sex shop owner David Nash, 47, from Durrington, West Sussex, was also convicted at Snaresbrook Crown Court.
The court heard how spyware was installed on computers at Sumitomo Mitsui bank with the help of an insider, who unlocked the doors at night to let the conspirators and their cohorts place keylogging software on user PCs.
The gang then gained access to user names and passwords relating to the holdings of major companies, including Toshiba International, Nomura Asset Management and Sumitomo Chemical UK.
They made several attempts to electronically transfer up to £12.5m at a time around the world, but were foiled by "field logging errors".
The security guard, Kevin O'Donoghue, and hackers, Jan Van Osselaer and Gilles Poelvoorde, both from Belgium, have already admitted their roles in the conspiracy.
Rodley, who lived in a Tudor mansion in Tewkesbury, Gloucestershire, was found guilty of conspiracy to defraud and conspiracy to transfer criminal property. Nash was cleared of the first charge but convicted of the second.
The court was adjourned to await sentencing.
A third defendant, Swedish national Inger Malmros, 58, was cleared of both counts.