HELP! Weird certificate showing up, have I been hacked?

Im getting this crazy certificate notification every time I try to access one of my sub-sites, see screenshot. I do not recognize any of the urls. Everything is running really slow, it must be a hack or attack of some sort but I do not know much about certificates. Any help diagnosing the problem would be appreciated.

Update:

I checked my registrar and my nameservers have not changed. I can access all of the sub sites in my multisite installation except the one that calls on this certificate.