Both Search for Extraterrestrial Intelligence (SETI) advocates, and UFOlogists have in the past disagreed, as to whether or not extraterrestrials have every visited, or are now visiting, the Earth. However, the search by SETI advocates continues.
The latest article which I have come across on SETI is from "Scientific American" magazine (click here for the magazine website) , volume 304 number 1, January 2011, pages 26-31. It is written by Tim Folger and titled "Space Contact the Day After."
"Within decades advances in computing power will allow astronomers to scan enough stars in our galaxy to have a reasonable chance at detecting a signal from an extraterrestrial civilization."
"News of the discovery of an extraterrestrial signal will reach the public almost immediately. A conspiracy to hide or suppress the evidence of an alien intelligence would be all but impossible."
"The content of the signal may never be understood. The assumption that mathematics or physics could serve as a cosmic lingua franca among civilizations may be misguided."
"Would revealing our existence to the universe at large attract the attention of hostile aliens? Such fears are probably groundless, despite the warnings of some prominent scientists."
One of these prominent scientists was Stephen Hawking (click here to read about this warning.)