Fragaria virginiana? I couldn't find a more specific name on that link but that's what came up with that name in a search. Looks like a match, but all of these kinds of plants look similar by leaf, at least to me. Many of the plants shown there are natives (for those of us in the US,) like F. virginiana. Looks annoyingly happy in your garden though, whatever it is. I thought Arlene was on the right track regarding getting rid of it.
