The Aliens are here, they are just very boring. Hundreds of Alien spies have been placed in all areas of the world but being so advanced they just get snapped up into business and industry due to the worldwide skills shortage. Once embedded into their work culture they realize it's much easier cruising through a 9-5 job than cruising through the galaxy with your Commander breathing down your to ''empty the space toilets!'' and ''shine up that anti-gravity drive!''.
The CIA discovered several Aliens working secretly at a data processing company, where they had formed a 'Keeping up with the Kardashians Fan Club' and joined a
Quidditch team, the Agency decided leaving them to carry on was the best punishment available.
Some entire model aircraft clubs are known to be Alien membership, 16% of all accountants are from the nebula G-es-tea, all taxation forms are clearly of Alien origin, lawn bowling clubs are maintained as emergency UFO landing strips.
The dullest profession the Aliens inhabit is of course politics, where they hardly need too camouflage their bizarre speech, mannerisms and features at all, luckily in our country it's efficient and dynamic public servants that really run the country.
So if you discover an Alien in your workplace, don't get panicked, take it out too a library or something fun, it could use the excitement.