I found this attractive flower while hiking through a forest in the Pacific Northwest this summer. The species is called Herb-Robert (Geranium robertianum). G. robertianum is native to Eurasia, but it has been introduced to the United States where it has been invading native forests and competing with the native plants [1].
Sources
[1] http://www.oregon.gov/oda/shared/Documents/Publications/Weeds/HerbRobertProfile.pdf