Make Your Site Look Like A Security Risk
There’s nothing like making your Web site look like a security risk to the general user:

Especially since those in the know recognize the domains as delivering ads. So one of the ads on the page under review triggers this alert, making it look to Joe Consumer like….well, who knows what evil malware/spyware/spam Joe Consumer would think this message represents? Regardless, Joe Consumer thinks your Web site is the problem.
Sometimes, developers mock up certificates for dev or test environments so the company doesn’t have to pay for an extra certificate. Sometimes, during deployment to production, mistakes happen. Did I say sometimes? I meant Always. Once in a while, they deploy an invalid certificate like this one.
How do you find this error? You look at the Web site. Which, and for the life of me I cannot fathom why this is, most people involved in developing Web applications or Web sites do not do. They leave it to QA, if they have QA, and to the client to find the obvious for them.
Meanwhile, Joe Consumer looks at this and thinks I just got a virus and never comes back to the ad-delivering Web site.