As best I can tell - this is not a plant I am personally familiar with (thank goodness!!) - it is garlic mustard, Alliaria petiolata.

It is definitely Alliaria petiolata, as GG says. A perfectly fine wild flower over here. Apparently a nightmare over there.

Info about management:

http://ext100.wsu.edu/whitman/2013/11/13/garlic-mustard/

I have that growing in a big patch of my yard. I pulled it by hand in early spring in spots where it was more scattered around. When it sent up the shoots, I sprayed about half of the heavily infested area with roundup rtu. They wilted a little and turned yellow but a lot of them were still ok and seem to be hanging on if not recovering. Then I busted out the weed wacker and chopped them down, top to bottom. You should do the same (weed whack/string trimmer) before they set seed and spread more. Cut them down from top to bottom so they get shredded up a bit. Be prepared to be absolutely covered in garlicy smelling plant matter. Wear safety glasses. All the plant mush I pulled out of the weed wacker shield would've made a nice garlic herb pesto spread lol. When all the other plants go dormant in late fall/early spring, this stuff will be hanging around close to the ground, and I've learned that is the best time to spray them with herbicide. Now that I am aware of this plant and it's blooming, I see it EVERYWHERE.