Change your modem password immediately. If someone knows your I.P address they can access your modem site. If your default is admin please change it. They will be asked for password. If they enter they can restart the modem deactivate wireless change settings and all the things that we do. You can know this by type your I.P in browser when typed the mode site open’s.
Visit this to get more details. http://www.thinkdigit.com/forum/showthread.php?t=57773