Drive-By Downloads

Can anyone give me a link or an idea of how to fix Drive-By downloads I have on a site I have created? Everything I search for online brings up how to repair an issue someone may have gotten on their computer from a drive-by download, but nothing talks about repairing it on the actual site itself. I don't have any injections or anything, but doing a check on my site from the norton site here shows that I have 1 Threat and it's on a contact form page due to Drive-By Downloads, is this from the php tags on the form not being stripped or from the javascript possibly?

 

Any help would be great, Thanks.