The AVM Runestone, also known as the Berg-AVM Runestone, is a hoax created in 1985 by students carving runes into a boulder near Kensington, Minnesota, United States, not far from the site where the Kensington Runestone was found in 1898.
In 2001, a carving expert and her geologist father found the AVM Runestone, told the press that it was proof of early Viking or Norse settlement in Minnesota, and began an investigation to prove its authenticity. The hoax creators came forward with their story that it was in fact purely a hoax and not an artifact of Viking explorers.
On September 5, 2001, Kari Ellen Gade, then chair of the Department of Germanic Studies at Indiana University, and Jana K. Schulman, associate professor in English at Southeastern Louisiana University, wrote a letter to the Minnesota Historical Society. They explained that in June 1985, when they were both students at the University of Minnesota, they and three friends, who chose to remain anonymous, had carved the AVM stone with a hammer and chisel, as a test of willingness to believe in mystery artifacts (and "for fun").
More information on the Wikipedia page 
See also Elbow Lake Runestone