Research In Motion (NASDAQ: RIMM [FREE Stock Trend Analysis]) shares are up more than 10 percent on very heavy volume (more than 2.8 million shares have already traded) in pre-market action Friday. The upside follows a 17 percent move higher on the Toronto Stock Exchange Thursday. While a number of sources are attributing the strength to a bullish research note from National Bank's Kris Thompson on Thursday, this is certainly not the full story. Thomspon boosted his price target on RIM shares from $12 to $15 amid increased carrier optimism related to BlackBerry 10 -- a factor also cited by Jefferies' Peter Misek Tuesday morning when he upgraded the stock to Hold. RIM shares were up nearly six percent on Wednesday.

Increasing sentiment in what may turn out to be RIM's Alamo is definitely notable; however, a $600 million swing in market cap...? That seems to be pushing it.

A more likely explanation for the sharp move higher: a short percentage which has been near 20% and bored traders looking for a liquid stock on Thursday while the U.S. stock market was closed. Also consider that RIM shares have nearly doubled since marking a 52-week low at $6.22 in September.

As is wise advice for any bargain shopper on Black Friday: buyer beware.

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