Take a look at some of Wednesday midday movers:
Athenahealth - The maker of billing and medical practice management software continued to fall after hedge fund manager David Einhorn late Monday said he was shorting the stock because the company was badly overvalued and could fall 80 percent or more off its highs.
Arris Group - The provider of media entertainment and data communications solutions rose after reporting better-than-expected quarterly earnings and issuing a strong forecast for its current quarter.
Chesapeake Energy - The producer of natural gas climbed after it posted better-than-expected first-quarter profits.
Cimarex Energy - The oil and gas exploration company rose after it agreed to buy oil and gas assets in Western Oklahoma for $497 million.
Datalink - The data center infrastructure and services provider declined after posting weaker-than-expected quarterly earnings and forecast earnings for the current quarter below street views.
Herbalife - The nutrition company that hedge fund manager Bill Ackman has called a pyramid scheme gained after it agreed to buy back $266 million of its stock from Bank of America.
King Digital Entertainment - The mobile game maker fell on worries the popularity of some of its products could be waning.
Lamar Advertising - The billboard company slid after posting weaker-than-expected first-quarter revenue.
Merck & Co. - The pharmaceutical company fell after Morgan Stanley downgraded the stock to equal weight from overweight.
Office Depot - The retailer rose after Credit Suisse upgrading the company to outperform.
Perrigo Co - The consumer healthcare products provider fell after posting weaker-than-expected quarterly earnings and lowering its full-year earnings outlook.
Siemens - The German industrial equipment maker rose after unveiling a restructuring plan.
Tim Hortons - The quick-service restaurant chain fell after missing second-quarter earnings estimates by two cents. Revenue also came in shy of expectations.
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—By CNBC's Rich Fisherman.
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