Tokyo (CNN) -- Investors were unable to trade shares in scores of companies listed in Tokyo for several hours Thursday after a computer problem at the city's stock exchange. The Tokyo Stock Exchange said it had suspended the trading of 241 securities, including shares of the electronics giant Sony, after problems with the exchange's market data systems. Tokyo is one of the largest stock exchanges on the planet by total market capitalization and has more than 2,000 listed stocks. The suspension began at 9 a.m. (7 p.m. ET Wednesday). A spokeswoman for the exchange said the affected securities had resumed normal trading at 12:30 p.m. (10:30 p.m. ET Wednesday). Sony was of particular interest to investors after saying Wednesday that its chief executive, Howard Stringer, would step down. The company's shares fell as much as 4.8% in afternoon trading. CNN's Yoko Wakatsuki and Jethro Mullen contributed to this report.
NEW: The affected stocks have resumed normal trading . The exchange attributed the trading suspension to problems with market data . The stocks include Sony, which has said its CEO is stepping down .