In a filing with the Securities and Exchange Commission, Aon said no misconduct by current or former management or directors was found, and the review is not expected to have a material effect on its reported stock option expense.
Procedures for stock option grants caused incorrect measurement dates to be used for financial accounting and tax purposes, Aon said.
Aon says it has taken remedial steps to correct the inaccuracies. The company is one of the two largest insurance brokers in the world.