In addition to Mr. Cohn, other longtime executives and engineers have departed in recent weeks, including a vice president of Latin American operations and the company's chief trust officer, who decamped to rival Google Inc.

WSJ: Yahoo Battles Brain Drain

But vagueness didn't prevent Northern Trust Chief Fiduciary Officer Hugh Magill, based in Chicago, from recently requiring a man in his mid-50s to prove he was "of sound mind, good moral character and temperate financial habits" as a trust for the man required.

WSJ: How to Control Your Heirs From the Grave

However, the market may struggle to build on those gains in the immediate future as traders and investors turn their attention back to Washington, said Ernie Cecilia, chief investment officer at Bryn Mawr Trust.

NPR: Stocks Drift Lower, Paring January Gains