“You’ve got to earn the right to be a conglomerate,” Peltz said in an interview. “The individual businesses need revenue growth similar to or better than their standalone competitors, and their margins better be best in class.”

The effectiveness of activism in recent years has emboldened usually passive institutional shareholders to increasingly back corporate changes. At Microsoft, ValueAct’s Mason Morfit and Jeffrey Ubben quietly garnered enough fund manager backing last year to gain a board seat and a say in the selection of a new CEO -- with a less than 1 percent stake. Microsoft shares have climbed 35 percent since ValueAct first disclosed its stake last April.

Diluted Stockholders

Some activist campaigns have hurt stockholders. Ackman’s Pershing Square exited its stake as J.C. Penney’s largest investor in August, after an effort to remake the retailer caused sales to plummet amid public spats and management reversals.

Over the course of Ackman’s three-year investment in J.C. Penney, the stock lost 58 percent, erasing about $4.6 billion in market value. Just weeks after Ackman quit the board and sold his stake, the troubled retailer issued stock that further diluted shareholders.

At ADT Corp., Corvex Management’s Keith Meister and billionaire investor George Soros urged the largest provider of home security to repurchase stock with borrowed money in late 2012. ADT ended up buying back shares specifically held by Corvex last November, and two months later the stock plunged because of disappointing earnings. Shareholders have lost 33 percent since Meister was paid to go away.

Activists can also be detrimental to bondholders. Their campaigns often involve returning cash to shareholders by increasing a company’s debt, according to Carol Levenson, director of research at Gimme Credit LLC in Chicago.

Wrong Advisers

“Credit quality suffers, spreads widen, cash that could have been used in productive ways for all stakeholders is siphoned off to one group of stakeholders, and the financial risk profile of the company weakens,” she said.

Illinois Tool Works, Timken Co. and SPX Corp. are among those that, while their stocks increased, had their credit ratings lowered or were considered for a downgrade after Relational’s Whitworth or Trian’s Peltz agitated for changes, according to a study by Joel Levington, an analyst for Bloomberg Industries.