Cannot explain increase in referral traffic from single domain. Doesn't even load when searched.

A website I'm working on saw a sudden huge spike in refarral traffic from a single domain: 'serving-sys.com'

I've tried searching for any information about this domain and apparently it is owned by Sizmek Technologies who seem to be some type of advertising partner with Amazon. I also read that it is a tracking cookie used for personalized ads and even saw it referred to as malware. I'm honestly not sure what the purpose of this domain is, why it caused such a sharp increase in traffic, and why it does not show up in referring domains, There's no specific link it's coming from just the domain as a whole.

I spoke with other departments at my organization such as advertising and PPC and they did not launch any recent advertisments (don't even use Amazon/Sizmek for ads) nor were they familiar with the domain.

Has anyone heard of 'serving-sys.com' that could shed some light?