Improper trading at ING U.S. was a case of mostly isolated incidents and did not represent a widespread problem, the maligned mutual fund firm announced Wednesday.

ING is currently under review by the Securities and Exchange Commission for "irregularities" in its trades. The company said its internal review will be released to all four million of its customers, both retail and institutional. The company also said that the trades had no huge impact on the company, and many occurred in subsidiaries before they were purchased.

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