I wanted to add to this that I have had my DNA checked and I did come up with .5 Scandinavian. Both sides of my family are pretty easy to trace since both my Mom and Dad's relatives were from some of the earliest settlers in the USA. The DNA test has been eerily accurate. The only relatives that are show as possibly being from Scandinavia are this line. Not saying it proves anything but thought I would put this out there.
The Vikings settled (conquered) many regions in the UK & Ireland as well as parts of France, Holland, Belgium, and the like. As such, Scandinavian DNA makes up part of the British population, and if you have British ancestors, then there is a good chance that the DNA testing companies will pick up traces of Scandinavia amongst your ethnic profile.