CHICAGO (Bloomberg) ? Aon Corp., the world's second-largest insurance broker, sold the bulk of its stake in Endurance Specialty Holdings Ltd., a Bermuda-based insurer it helped found after the September 11 terrorist attacks.

Aon, based in Chicago, sold 9.8 million shares of Endurance in a block transaction with Goldman Sachs Group Inc., Endurance said today in a statement. The broker had 9.9 million shares as of September 30. Aon spokesman Al Orendorff declined to comment.

The sale, which would generate $338 million at today's closing price, follows criticism by New York Attorney General Eliot Spitzer that brokers may have created a conflict of interest with clients by investing in insurers.

Endurance didn't disclose terms of the sale. Spokeswoman Marianne Walsh didn't immediately return a voicemail message.

Aon also owned 4.1 million of Endurance stock purchase warrants as of September 30, which it valued at $71 million, according to a quarterly regulatory filing. Thomas H. Lee Partners LP and Texas Pacific Group are among Endurance's other shareholders.