[mongodb] MongoDB: Server has startup warnings ''Access control is not enabled for the database''

I firstly installed MongoDB 3.4.1 today. But when I start it and use MongoDB shell, it gave me these warnings below:

C:\Users\hs>"C:\Program Files\MongoDB\Server\3.4\bin\mongo.exe
MongoDB shell version v3.4.1
connecting to: mongodb://127.0.0.1:27017
MongoDB server version: 3.4.1
Server has startup warnings:
2017-01-12T21:19:46.941+0800 I CONTROL  [initandlisten]
2017-01-12T21:19:46.942+0800 I CONTROL  [initandlisten] ** WARNING: Access control is not enabled for the database.
2017-01-12T21:19:46.942+0800 I CONTROL  [initandlisten] **          Read and write access to data and configuration is unrestricted.
2017-01-12T21:19:46.942+0800 I CONTROL  [initandlisten]

my computer is Microsoft Windows [version 10.0.14393].

Mongodb v3.4

You need to do the following to create a secure database:

Make sure the user starting the process has permissions and that the directories exist (/data/db in this case).

1) Start MongoDB without access control.

mongod --port 27017 --dbpath /data/db

2) Connect to the instance.

mongo --port 27017

3) Create the user administrator (in the admin authentication database).

use admin
db.createUser(
  {
    user: "myUserAdmin",
    pwd: "abc123",
    roles: [ { role: "userAdminAnyDatabase", db: "admin" } ]
  }
)

4) Re-start the MongoDB instance with access control.

mongod --auth --port 27017 --dbpath /data/db

5) Connect and authenticate as the user administrator.

mongo --port 27017 -u "myUserAdmin" -p "abc123" --authenticationDatabase "admin"

6) Create additional users as needed for your deployment (e.g. in the test authentication database).

use test
db.createUser(
  {
    user: "myTester",
    pwd: "xyz123",
    roles: [ { role: "readWrite", db: "test" },
             { role: "read", db: "reporting" } ]
  }
)

7) Connect and authenticate as myTester.

mongo --port 27017 -u "myTester" -p "xyz123" --authenticationDatabase "test"

I basically just explained the short version of the official docs here: https://docs.mongodb.com/master/tutorial/enable-authentication/

You need to delete your old db folder and recreate new one. It will resolve your issue.