Wireless LAN (WLAN/WiFi) will be in Enabled state by default in the Modem/router provided by BSNL.
Someone can use your broadband if it is in Enabled state. You have to disable it or restrict it using MAC filter.
Find below the steps for disabling Wireless LAN in Modem/router (WA3002G4) provided by BSNL.
1. Type http://192.168.1.1/ in the browser address bar and click 'Go'/press Enter.
2. Enter username and password in the pop-up Dialog. (Mostly for bsnl it will be admin/admin)
3. Click 'Wireless' in the left side menu.
4. Uncheck "Enable Wireless" checkbox and click "save/apply".
Note that this will disable wireless Lan completely. Suppose if you want to enable Wireless Lan only for specific computer or for your laptop you can do it by following below steps.
1. Do first 3 steps in the above mentioned procedure. And make sure that "Enable Wireless" is checked.
2. click "MAC filter".
3. choose "Allow" for MAC Restrict Mode.
4. Click "Add".
5. Enter MAC address of your laplop/computer and then click "Save/Apply".
If you don't know the MAC address, follow below steps to know MAC address.
1. Type "cmd" in Start->Run to open command prompt.
2. In command prompt type ipconfig/all.
3. look for physical address in the response for ipconfig/all.
4. The physical address will be a 12 digit alphanumeric having hypen in between them. Replace the hypen with colon (:) when entering it as MAC address in bsnl modem/router.