Apple (AAPL) shares were higher in midday trading Monday after activist investor Carl Icahn said the company was undervalued and worth almost double its current price. Icahn also encouraged CEO Tim Cook to accelerate buybacks. Chinese microblogging site Weibo (WB) plummeted more than 7% after Summit Research downgraded to HOLD. Alibaba (BABA) was lower after luxury clothes maker Kering filed a suit against the e-commerce giant, alleging it allowed counterfeit versions of its brand on the site. BHP Billiton (BHP) tumbled after the company's South32 spinoff was valued at just over $9 billion, the lower end of expectations.
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