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.
Qihoo 360 Technology - climbed after the company said a deal with Apple is forthcoming.
Walgreen - Shares of the drugstore chain edged lower after it said it would fill prescriptions at no upfront cost to patients who don't have all the information they need for coverage received through the health care overhaul.
D.R. Horton - Shares of the homebuilder climbed after Sterne Agee called it one of its top picks in the sector.
Voxeljet - The German provider of three-dimensional printers gained on market speculation it could be acquired by 3D Systems.
Patient Safety Technologies - The supplier of medical products rose after Stryker said it would buy company for $120 million, or $2.22 a share, a 50 percent premium from the stock's closing price on Monday.
Marathon Petroleum - Its shares rose along with other energy stocks, led by refiners. Valero Energy and Tesoro also gained.
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—By CNBC's Rich Fisherman.
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