Shares of Sun Microsystems ( SUNW) thrilled to a rare pop today, jumping 8% on rumors the troubled server and storage maker might be acquired. But analysts threw cold water on the takeover story, while a trader said the strength likely stemmed from a massive institutional buy.

The stock rose 27 cents, to $3.61, in early afternoon trading, on heavy volume. Nearly 62 million shares already were changing hands, compared with average daily volume of 48 million, according to Baseline.

At UBS Warburg, Jack Francis, co-head of equity trading, said the sudden surge in price followed a 5-million-share block trade, considered to be a very large buy by Wall Street standards. "That was spurring stories of a potential takeover, which doesn't make any sense at all but did add fuel to the upside," said Francis. "The rumor doesn't hold a lot of weight, but in a market like this it gets people off the fence who are looking for any story that could generate alpha."

Further undercutting the acquisition theory, shares of both IBM ( IBM) and Dell ( DELL) -- both named as likely acquirers -- traded up Friday. Typically the stock of an acquiring company would trade down. H-P ( HPQ), viewed as a less likely acquirer since it's still digesting its purchase of Compaq, was also gaining slight ground.