Investment agitator and former corporate raider Carl Icahn today tossed in the towel in his fight to get Apple to boost its share buyback program by another $50 billion after an influential proxy advisory service nixed the idea.

The white flag put an end to a months-long campaign by Icahn that some analysts said was at best a distraction to Apple, at worst trouble -- the kind with a capital "T."

"Icahn likes to lean on you to earn more money for himself," said Ezra Gottheil, an industry analyst with Technology Business Research who covers Apple.

Icahn gave up on his bid to convince Apple to increase its already-large buyback fund in a message on Twitter today that pointed to an open letter published on his Shareholders Square Table website.

"While we are disappointed that last night ISS recommended against our proposal, we do not altogether disagree with their assessment and recommendation in light of recent actions taken by the company to aggressively repurchase shares in the market," Icahn wrote.

ISS, or Institutional Shareholder Services, is a Rockville, Md.-based research firm that advises large institutional investors. Over the weekend, ISS issued a report to clients that said Apple's recent efforts were sufficient and that the company and its board should not be handcuffed to a micromanaged plan.

Icahn also noted Apple's recent $14 billion buyback, which CEO Tim Cook announced last week in an interview with the Wall Street Journal (subscription required) as a reason for withdrawing from the fight.

In that interview, Cook said Apple was "surprised" by the 8% plummet in its stock price the day after its Jan. 27 earnings call for the fourth quarter of 2013. The share price fell an additional 1% before beginning a climb on Jan. 31. Cook told the newspaper that the firm was "opportunistic" in buying back shares at the depressed prices.

"In light of these actions, and ISS's recommendation, we see no reason to persist with our non-binding proposal, especially when the company is already so close to fulfilling our requested repurchase target," Icahn said.

Cook also used the Wall Street Journal interview to make his most public promise yet that Apple would enter new product categories -- which analysts and other observers have interpreted to mean something more than just expansions of its iPhone or iPad lines -- but as always, kept cards close to his vest, revealing nothing about timing.

He had alluded to new product categories in the January conference call with Wall Street, as well.

Icahn had mentioned new product lines -- including televisions and wearable devices -- in a missive he penned last month when he urged Apple stockholders to vote for the non-binding proposal he placed on the agenda for the Feb. 28 shareholders meeting on the company's Cupertino, Calif. campus.