In Internet Explorer (nearly all versions except IE 5.01 on all supported Windows operating systems) there is a vulnerability which Microsoft issued a warning about. Attackers actively abuse the security hole to smuggle malware on PCs. To infect a machine, following a link to a specially crafted web site suffices.
It seems that this security vulnerability was used to attack Google in China. This is likely as Microsoft lists Google as contributor in the advisory. The problem exists as “in attempting to access a freed object, Internet Explorer can be caused to allow remote code execution. ”
It seems like a good idea to use alternative Web browsers like Firefox, Opera, Chrome or Safari in the meantime.