It started in Germany, during the twenties and thirties, when the theories of the Ayrian race began to develop,and glamorous pics af the Ayrian people were produced.
I guess Hollywood has a part of it too, not to mention reenactors and Swedish Ice Hockey fans wearing blue/ Yellow horned helmets watching the Ice hockey World Championships, ( when Sweden whippes the US team in the final.) hehehehe
There is only one helmet found in Scandinavia ( Norway), and it did not have horns. http://www.angelfire.com/wy/svenskildbiter/armsandarmour/mailshrt.html
I found a Swedish document on the web about the myth of Viking horned helmets. It is named " A study of the non- existent"
But ......There are exceptions: American Vikings still have horns on their helmets - and they are existant !
/Knut