wifi doesn't need a password any more

My tenants say that my wifi doesn't need a password any more. When I remotely check my router everything is fine: the SSID is ok and the password is required.

Also, they said that an SSID appeared it was the same as mine except with a 2 at the end.  

Is someone trying to hack their devices from near by my house?

Some advice on what to do would be great.