The Department of Homeland Security issued an advisory Wednesday urging people to immediately apply a security patch for vulnerabilities in all supported versions of the Microsoft Corp. Windows operating system. Windows is the No. 1 operating system for personal computers in the world. "From time to time the Department of Homeland Security has issued advisories on Microsoft security bulletins," Microsoft said. So far Microsoft knows of only one or two attacks. The MS06-040 advisory involves several vulnerabilities which, if exploited, could allow a hacker to install programs, view changes, delete data or create new accounts with full user rights.