Take a look at some of Tuesday's midday movers:
Hertz Global Holdings - The car-rental company's shares jumped. CNBC reported that activist investor Daniel Loeb's Third Point Capital had taken a less than 5 percent stake. On Monday Hertz said it had adopted a 'poison pill' after observing unusual and substantial activity in its shares.
Amazon.com - Shares of the online retailer gained after Citigroup raised its price target from $381 to $457 a share and maintained its buy rating.
Twitter - Shares of the social-media company rebounded after falling 13 percent last week on a downgrade from Macquarie.