Warning: Execute this hack at our own risk.

Nowadays isp's are binding the user accounts to the modem/router's physical address so you may also have to refer to my post which explains "how to spoof your modem /router's mac address to match other user's account " [link].

Also note that MTNL still does not bind the user account to the router's physical / Mac address so the hack works on it with ease.

I have written this post after both successfully cracking both Airtel and MTNL accounts and have operated my broadband at 2mbps while paying for only 256kpbs, But i did not overuse any account that's what you should remember or else you will be caught.

The steps are as follows:-

1. first go to any site that tells you your ip address or you can also
know this by logging into your router/modem .
http://www.ip-adress.com/

2. copy and paste the ip address on the address bar of the browser
just delete the last part of the ip. Like this

lets say your ip is 122.163.22.7
now you can change the last part to 122.163.22.1 to 122.163.22.200

3. goto browser window and paste ex 122.163.22.2/main.html
It will ask for userid and password type userid="admin" passwd="password"

4. goto wan setup and then choose edit

5. Skip the vpi ,vci part goto ppp.username and ppp.password page
now this is the tricky part but not that tricky :)
just right click and select "view frame source"
and voila! on that page you have id and password of nincompoop users
who donot protect their routers with a different password .

6. apply this username and password setting on your wan setup page of your router
that is 192.168.1.1/main.html page save and reboot and there you are
using someone else's account. :)

7. You should keep changing the last octet of ipaddress it will work for some account.

Below are the snaps showing one of my hacks so enjoy. :)