Blackboard (BBBB) shares soared 29% yesterday after the company said it has received unsolicited takeover offers.

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It then rejected an unsolicited takeover bid made Feb. 15, and--on Friday--rejected a second bid made on Feb. 19.

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Then Bass launched an unsolicited takeover bid for the rest of the company and sued it in an effort to increase his share of its dividend payments.

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Calpine received an unsolicited takeover approach from NRG Energy.

ECONOMIST: Business this week | The

Ralcorp, you might recall, rejected without negotiation unsolicited bids from ConAgra ( CAG) and adopted several measures to make further takeover attempts less likely.

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