Best Buy Bombs, Blackberry's Bummer, Markets See-Saw on Global News

Stocks moved lower in midday trading Thursday with the S&P, Dow Jones and Nasdaq all down. Nasdaq leading the way, losing about 0.7%. Best Buy said it posted improved comps for the holiday season -- but disappointing guidance could not be overlooked by investors with the stock falling about 13% in midday action. And BlackBerry shares soared yesterday on a report that the company, and Samsung, are contesting: one media report pegged Samsung as the smartphone maker's buyer, but neither was willing to cop to it.