Abnormal ADSL Broadband Usage

[Nimalkad]

I use a SLT Broadband connection in my Windows XP. As of late, I notice that my usage( as displayed in the statistics of data received/sent )is getting abnormally high although I am a sure it can't be that high. I mostly use it for browsing text based sites. Connection speed is normal.
For example, in a 10 minute interval of light and intermittent browsing without any graphics or downloading files,the bites received can be as high as 1 M Bytes. This is definitely in quite contrast to what I used to have in the past.

I have installed  AVG ( free) and switched on Windows firewall also.

I suspect probably a virus is tampering with  my connection.Is this a likely cause. If so,what can I do about the problem? I am thankful to receive some help/suggestions.

[Saman]

It can be a spyware. Use Malwarebytes Anti-Malware. I remember they provide a trial or free version.

Spybot is another great free spyware removal tool.

Hope this will help!