The FBI recently released documents of alien existence...on the internet. It's called a "soft leak", and that's when they release information through ways that wouldn't have the entire U.S. panicking.
Other countries already told citizens about alien existence, but by making a big ass speech or press conference about this on the news, surely people would go ape shit.
The FBI has an online database of all their documents, called "The Vault".
Read it and weep;
http://news.yahoo.com/s/ac/20110411/...cret_ufo_memos