Help Identify this strange plant with purple/black fruit

Hi everyone, I have been searching through the info on this site & have not had any luck identifying this plant that sprouted up in my garden. I usually wait awhile in the spring before I start weeding as I have had various herb & vegetable plants come back from seeds that were dropped the previous season so I left this thing alone when it started growing. It's flowers are tiny, nightshade like, and the berries are green then turn dark purple/black. The black ants have been swarming on the plant, eating the leaves & possibly damaging the stems of the berries. (there's black stuff around the stems of the very ripe berries)
When I cut open a berry it is greenish, full of little seeds & smells like a green tomato.
What the heck is it?? Can I eat the berries? Should I pull it out?

Thanks so much!!

 

Solanum americanum – American Black Nightshade?
http://www.fallbrooksource.com/gallery/2/b/solanaceae/solanum americanum/index.html

 

Thank you so much for replying! This is exactly what it is. I wonder how it got into my garden?

 

Birds are the most likely culprits.