[{_id:123,Customer:"A",State:"TX",City:"Houston",checksum:1111,IsBundlled:1},{_id:1234,Customer:"B",State:"TX",City:"Houston",checksum:1111,IsBundlled:1},{_id:12345,Customer:"c",State:"NY",City:"Buffalo",checksum:2222,IsBundlled:1}]

db.collection.aggregate([{"$group":{"_id":"$checksum","toUpdate":{"$addToSet":"$_id"},cnt:{$sum:1}}},{$match:{cnt:{$gt:1}}},{$unwind:"$toUpdate"}])