Microsoft acknowledged Tuesday that malicious software targeting an unpatched bug in Internet Explorer is on the loose, and urged users to run a complete system scan on its new Windows Live Safety Center -- which has a quirk of its own -- to detect and delete the code. In an update of a security advisory issued Nov. 21, Microsoft noted that both proof-of-concept code and an exploit are in circulation. The exploit can compromise PCs running IE on a host of the company's operating systems, including Windows 98, Windows Me, Windows 2000, and Windows XP. The bug, which was reported...