Did they pay a dividend or something (do they pay dividends?). According to my brokerage, CYB has dropped 2% today. According to Yahoo it is up slightly. Also according to Yahoo it was 25.7 yesterday and 25.1 today, a 2% drop.
They paid a dividend of about $.55 (ST and LT cap gain). Go to http://www.wisdomtree.com/about/pdf/WisdomTree-ETFs-Declare-Quarterly-Distributions-2011-12-795.pdf for more info.