[ Thanks to An Anonymous
Reader for this link. ]
“The activity sparked an investigation with the collaboration of
the companies sending the data to the data center in question. It
turns out the activity was due to user’s machines being infected
with malware meaning Google could detect individual machines that
carried this infection just by flagging the activity patterns.“The detection is possible because the malware being used
accesses Google through a set number of proxy servers. So when
Google notices traffic through one of these proxies it knows the
machine sending the request is infected with this strain of
malware.”