Question for Mar 10, 2010

The term X entered the Oxford Dictionary in 1990, though the term was known for more than a decade prior to that. In 1976, Doug Bower and Dave Chorley conceived X as a prank, and in 1978, using planks, rope, hats and wire as their only tools, created X. When this did not receive significant publicity, they repeated it in 1981. When it was claimed that X was due to natural phenomena, the two created more and more complex versions of X. Others created their own versions of X, which led to groups of people attributing extra-terrestrial or other paranormal activity as the source of X, even in the face of documented proof of a human hand in X. In 1999, a researcher studied X, and concluded that 80% of all X were man-made, but could not account for the remaining 20%. The controversy over its origin continues to rage.

Identify X.