Basic materials are leading the gains as stocks advance modestly in midday trading Friday after surging in the past 2 sessions. It's also a quadruple-witching day so, trading may be a bit more choppy as stock, index options and futures contracts expire. Shares of Sony (SNE) are trending lower. U.S. authorities formally accused North Korea as being behind its devastating cyber attack. The FBI determined North Korea is responsible for the hack, by way of Chinese computer networks. On Wednesday, Sony canceled the release of its film 'The Interview' after threats were made against movie goers. Earnings results are driving stocks higher in the session. Red Hat (RHT) is jumping nearly 12% after reporting positive revenue and guidance. Used-car seller, CarMax (KMX) is reaching almost 10% higher on better-than-expected results.