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I am connecting to the Internet with a modem. The tariff I have has a transfer cap; it is a limited package. My latest bill was five times more than what usually I get, even though this time I used it much less than usual.

I am sure somebody else is using my connection. How can I find out who it is?

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If you're using a modem directly connected to your computer, and don't have a wireless router or access point, ask your family members. – Daniel Beck Dec 31 '10 at 11:13
a cable/dsl modem or a telephone modem? – Nifle Dec 31 '10 at 11:40
Is your bill calculated by connect-time or transferred-bytes? – harrymc Dec 31 '10 at 13:59

If you''re using dail-up modem, then you should check with your Internet service provider to see from which phone numbers your account was accessed. If strange number shows up, change your username password and check your computer for malware.

If it's all from your computer, then check with other users. I you'd tell us which oeprating system you're using, we might be able to give you more specific advice on how to see when your connection was used.

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windows operating system – vijay Dec 31 '10 at 12:48
which version of the windows operating system? – Matthieu Cartier Dec 31 '10 at 13:17
@vijay If you don't know which version of Windows you are using, restart the computer and while it is turning on, note what is says on screen. At one point it is going to say windows and something else. Write that down and tell us. – AndrejaKo Dec 31 '10 at 14:41

Without knowing what your network looks like, it will be difficult to provide recommendations. You probably have a wireless router that either has no security or is using WEP. Stop using WEP. Change your security keys.

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using modem connection and it is not wireless router can u please suggest me which tool i need to use to track – vijay Dec 31 '10 at 11:10
thanks for u r response – vijay Dec 31 '10 at 11:11
What kind of Modem???? Edit your original post to include more information for an informed answer! – Moab Dec 31 '10 at 15:39
It is difficult to tell from your comments and changes to your question what your actual configuration looks like. It seems like you are using a dial-up modem and not a cable or DSL modem. If that is the case then you'll need to contact your ISP to see what telephone numbers have accessed your account. If that's not the case then you have shared your computer with other users and they are responsible OR you have some sort of malware that has made your computer part of a zombie network. Regardless, more and clearer information from you would help us help you. – Mike Chess Dec 31 '10 at 16:57

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