Authentication failed for user user from IP 216.250.125.170; bad username or password.

[arun]

I installed Free file sync and for making my system as SFTP server I install free version of Solarwinds SFTP/SCP utility.

It is working fine because I have tested it for one user. But in between it is showing status like

Authentication failed for user user from IP 216.250.125.170; bad username or password.

And some times user name changed to admin, ubnt, root, test, guest and some time IP gets changes for the same users.

Please tell me there is any intruders in my system or In my network ?