I work for a certain intelligence agency from a certain country, and I got to see some pretty interesting documents. Some of the interesting things I read was:
1. Flying Saucers, abductions and "grey" aliens are real
2. Aliens appear to be scientists, and they do not want to communicate with any government or military
3. They do not want to be seen, and when we detect or chase them, they go away
And perhaps the most interesting info:
4. In the past, after several attempts, intelligence agents successfully "baited" aliens to abduct themselves so they could observe/study the phenomenon. They managed to get a great deal of important data (which I didn't have access to).
5. Some of those agents never returned from the abduction

The conclusion of the document says that the phenomenon is real, and the political impact of a disclosure would be too strong, where some countries could adopt an aggressive posture against alien craft, which could make aliens avoid us.

The funny thing is, this document that I've read is pretty old, and it's not even part of the most secret ones, and I'm pretty sure at least a few thousand people around the world have access to it.