It's actually not any known Mac malware. It may be some kind of adware, although it's not a site I've heard of being associated with any of the adware I'm familiar with. It could also be a network issue or a hacked router. See:
The difference between malware and adware is subtle, and sometimes adware crosses the line. Adware is typically just designed to shove ads in your face, but doesn't actually do truly malicious things like steal your data or give remote access to your system.