Microsoft Corp. warned users of its Windows operating system on Tuesday of three newly found "critical" security flaws in its software, including one that could allow attackers to take complete control of a computer. Computer security experts urged users to download and install the patches, which are available at www.microsoft.com/security. "Users (should) apply the updates as quickly as possible," said Oliver Friedrichs, senior manager of Symantec Security Response, part of security software company Symantec Corp. SYMC.O. Microsoft said that vulnerabilities exist in its Internet Explorer Web browser, the most severe of which could allow an attacker to take complete control...