Microsoft Windows users need to watch out for several flaws in non-Microsoft media players, security experts said. Apple Computer and RealNetworks have both issued fixes for their Windows software to patch serious security vulnerabilities. Apple released Quicktime 6.5.2 on Wednesday to plug two holes in its Windows media player. On Tuesday RealNetworks advised users of its RealPlayer 10, RealPlayer 10.5 and RealOne Player software to use the “Check for Updates” feature to download the latest patch.