URL Blocked because of Malware but validation sites say the URL is ok

Hello Symantec,

Our SWG is blocking a URL because it's considered a known malware domain "expediteper.web713.discountasp.net" but other web validation sites say it's ok.  Here's some examples:

Norton Safe Web
https://safeweb.norton.com/report/show?url=web713....

McAfee SiteAdvisor
http://www.siteadvisor.com/sites/expediteper.web71...

ScanURL.net
http://scanurl.net/?u=expediteper.web713.discounta...

Why does SWG classifiy it differently?

Thanks,
Todd