Here is the source of the issue:

https://github.com/mongodb/node-mongodb-native/blob/1.4/lib/mongodb/connection/url_parser.js#L25

It seems that '@' is valid character for password, for instance:

mongodb://user_123:user@123@mongohosting.com:12345/test

So auth part: auth_part = connection_part.split("@")[ 0 ];
will end with: user_123:user
And connection part: connection_part = connection_part.split("@")[ 1 ];
will end with: 123@mongohosting.com:12345/test