Updated with stock prices and analyst downgrade info.By Fred Fuld Revenue and earnings surprises can cause stocks to make sharp moves upwards, which in turn can set off a short squeeze as short-sellers rush to cover their bearish positions. For example, after Palm ( PALM) announced better-than-expected sales and lower-than-expected losses on June 25, it rose more than 12% in after-hours trading, causing short-sellers to be squeezed. A short squeeze occurs when short-sellers quickly buy in shares of a stock, driving the price of the stock up sharply. The ratio for measuring short-squeeze opportunities is the short ratio, which is the number of days it would take the short sellers to cover their position based on recent average daily volume. With Palm's recent move in mind, Stockpickr has reviewed the heavily shorted tech stocks with market caps of more than $500 million and created a portfolio of the top financial short-squeeze plays, including Blackbaud ( BLKB). To read more, visit Stockpickr.com.