Hedge fund manager William Ackman told investors he has had three "failures" in his portfolio over the years, all retailers, and retail investing has not been his "strong suit."

He included J.C. Penney, where he is sitting on hundreds of millions in losses and left the company's board last week, as one of the three failures. Borders Group and Target are the others. Ackman made the comments in an investment letter dated August 20 seen by Reuters.

He said he may choose to exit Penney "after more or less time depending on developments at the company, the stock price, and the availability of other investment opportunities."

He is the company's biggest shareholder.

In the past he has sidestepped questions from investors about what he would do with J.C. Penney as his investment is now at a 40 percent discount to where he bought it three years ago.

Herbalife, where Ackman has a $1 billion short bet on the nutritional supplements company which has lost roughly $300 million so, ranks in the "undecided column," the fund manager said.

Serious product quality issues plus timely aggressive regulatory intervention may still save the day on Herbalife, he said, declining to give more details about which regulators may be probing the company.

Reviewing his nearly 10 years at $11 billion Pershing Square Capital Management, Ackman said 16 of 19 investments have been successes on the long side while the bets on Borders Group, Target and J.C. Penney are grouped in the loser column.

"We have had three failures on the long side," Ackman wrote, citing the companies and adding "Clearly retail has not been our strong suit, and this is duly noted."

Bets on Wendy's International, General Growth Properties and Canadian Pacific Railway, among others, have been winners on the long side while he won big on the short side with bond insurers MBIA and Ambac.

Apart from the three listed "failures," Ackman said "our active investments (have) done extremely well during our holding period."