Federal investigators believe the fraud in the investment management division and advisory division may have begun in the 1970s. However, Madoff himself stated his fraudulent activities began in the 1990s. Madoff's fraudulent activities are believed to have accelerated after the 2001 change from fractional share trades to decimals on the NYSE, which cut significantly into his legitimate profits as a market-maker.
Alerted by his sons, federal authorities arrested Madoff on December 11, 2008.