One of the more useful assets available to CETT, not to mention one of the greater possible threats it faces, is a rather secretive species called the "Fox-folk" (if they have a personal name, they haven't let any outsiders know about it).
On the one hand, they possess a unique set of skills that can serve an anti-alien paramilitary black-ops quite well, with their abilities to at blending in with crowds, their connections on the fringe of society, and combat abilities not normally available to human troops. On the other, they are probably the oldest xeno-infiltration unit still lurking amongst Earth's population.
While their origins are cloaked in myth, and CETT is ever watchful for the day when their "masters" might show up, for now these vulpine humanoids are few enough in number (and apparently content with hiding in the shadows of the urban landscape) to not pose an immediate threat.
Just as long as you meet their price, and/or peak their interest, you can at least expect high performance in their field of expertise.
As mentioned, the precise origins of the Fox-folk are known only to themselves, and there seems to be a silent agreement amongst them to keep things that way. However, a number of astute archeologists have theorized that they might have roots as far back as the earliest days of human civilization, with possible connections to multiple legends in animism pathologies, the most well known being the kitsune of Japan, although there have been some who also made links to European folklore, such as Reynard of France, and the enigmatic Huldra of Sweden (though the last link is tenuous at best).
As for the modern world, all that is known about them can be found in official (classified) government records, which are spotty at best, due in no small part to '98-'99, which destroyed a great deal of collected databases worldwide.
[Clascsins--75-23 It has been confirmed, however, that what records that did survive where intentionally tampered with. As such, CETT is keeping an even closer eye than normal on Fox-folk activities. However, need trumps suspicion, and usage of vulpine agents doesn't seem to be ending anytime soon.
One of the most intriguing things about Fox-folk is their interactions with humans and each other. Generally Fox-folk are friendly, amiable, courteous, and quite comfortable in large crowds, at least as long as the crowd made up of humans. In fact, despite apparently being an infiltration unit, some can be quite the attention seekers, with a few taking up lives in front of the camera (or even behind it).
However, the times when more than six are in the same general area are surprisingly rare. While this would seem suspicious at first, there is actual scientific evidence, including a rather interesting experiment performed in the waning days of the Soviet Union, pointing to a more mundane explanation: they just can't stand each others' company. Why this is up for much debate, and there is some question that they might be putting on an act, but for those in the know it's just an interesting bit of trivia, one that also seem to connect to another oddity about them: they don't seem to have a "culture" of their own, instead preferring to integrate themselves into human culture as a whole, although this could be an element of their infiltration nature.
(more later, currently distracted)