We’ve all come across “believers” in our day-to-day lives. Some of you probably have family or friends who believe aliens visit our pale blue dot on a regular basis. Some even go as-far-as to say that various governments from around the world are working in secret with extra terrestrials to advance their own agenda. So let’s take a few minutes to explore these possibilities.
The idea has all the earmarks of a conspiracy theory*, but offers no explanation as to why the aliens would go along with such a thing. Any civilization that could travel a minimum of 4 light years to get here would be no respecter of regional governments. I also don't believe they'd be coming to acquire any resources, so there'd be no need for contracts with suppliers for material (i.e. "unobtanium" a la Avatar). There are no gaps in the periodic table and no element would be easier to get by traveling to another star system. If you didn't have enough of a certain rare material, it would still be easier to make it one atom at a time in a particle accelerator, or nuclear reactor, than traverse the cosmos looking for a place to mine it. I’d suggest a similar answer to the using-humans-as-slave-labor theory as well. They would have mastered robotics and AI to be sure.
No, if they came at all, extraterrestrials would come for cultural reasons. They'd be eager to talk to the best authors, musicians, poets and even scientists (to understand our current level of knowledge). As far as I know, most of those people wouldn't agree to keeping that secret, even when asked by their local governments.
Finally, secrets are harder to keep than most people seem to think. I remember a panel I attended at Dragon Con a few years ago where a fellow had taken his telescope/clock drive and attached it to his computer. He used it to take and make enhanced images of the space shuttle docked at the International Space Station. He then published pictures of it on his website. The "guys in the black suits" (AKA the FBI) came knocking on his door. He said they were incredibly polite and even cordial about it. They simply said that they had no idea that a private citizen could develop that kind of capability and wanted to know how he did it. They made it clear he'd broken no laws. They were simply impressed and wanted to know how easy it would be for other governments to do the same thing. If the star ship Enterprise were in orbit over the earth, some backyard astronomer or asteroid hunter would stumble upon it. And then of course, there's Edward Snowden. It's simply a secret that is too big. No government could keep for 50 years.