Is the common thread that everyone this has happened to is using Safari? And are you using a Mac product? I read something recently about an iTunes update breaking Safari. No sure if this is related or not, but I do know that UKS currently has a clean bill of health from Google.

Security Issues

Currently, we haven't detected any security issues with your site's content. If you want to learn more about security issues and how they could affect your site, review our resources for hacked sites.

However, if you see a malware warning in the browser when navigating to your site, it's likely that your site is referencing code or content from another domain that has malware.
meaning, I think, there is a link on UKS to a site that has Malware, and that could be literally ANYTHING from a link to an old sponsor to a photo sharing site to a blog link....

So we need to determine if all the people who are having problems are all doing so because they share something other than UKS. And it seems like Safari has been mentioned in a few posts. But if you can all post what device, browser, and OS you are using that would be helpful for others.