Health-care technology company Athenahealth and its colorful chief executive Jonathan Bush have contended with critics in the past. But now they face their first major activist in Elliott Management – one with a track record for rebooting management and selling companies.

Elliott disclosed a 9.2 percent economic exposure to Athenahealth's common stock on Thursday through ownership of shares and derivatives. Shareholders applauded the investment, sending the stock 22 percent higher in Thursday trading.