While Windows and other Microsoft Corp. products are the favorite targets of hackers, the malicious code writers are increasingly targeting software that run on other operating systems, including Apple Computer Inc.'s Mac and open-source Linux, a security research group said Monday. In its list of the top 20 most critical Internet vulnerabilities in the first quarter of the year, the Sans Institute reported that software fixes were released for flaws in RealNetworks Inc.'s RealOne Player and RealPlayer. Security flaws were found in versions of the multimedia players running on Windows, Mac OS and Linux. In addition, vulnerabilities were listed for...