Something Downloading in the background

[stellar]

I have a wireless internet connection and whenever i use it for chatting only something is downloading in the background coz using chat doesn't eats up that MB of bandwidth. In 5 min it shows 5 MB download in the receive/sent connection icon. How can i see where the download is taking place. I have even turned off automatic updates too. Using Windows XP firewall also on and Norton antivirus didn't also found out nothing malwares,so did spybot.

Should i be switching to Private connection when logging to the net using the wireless connection?

My system also restarts abnormally.should i reinstall xp again.

[pushkar]

Definitely a malware problem. Install a firewall like Comodo or Sygate which will tell you which applications are trying to connect to the internet. If you see any unusual program in the list, block it and see if the bandwidth usage lessens. Also, install Security Task Manager and run it. It will show potential dangerous applications at the top in red colour. But just because it's red doesn't mean it's dangerous, so be careful when deleting or ending processes.

I don't think Norton will be any helpful. I have used the 2009 Internet Security and it failed to detect any viruses when Kaspersky on the same machine detected a lot of them later.

Also try MalwareBytes Anti Malware and do a full system scan on all drives. It has been pretty good to me in finding unwanted malware. Also, install a decent anti-virus like Kaspersky, Nod32 or Avira.

If you do choose to reinstall, please keep in mind that if you don't format the drive, or if there are other partitions in your system, the viruses may crop up again in the new installation. So you need to do a clean reinstall with all partitions clean.

Edit: There is also Wireshark, an application which can give some advanced details about network usage. See if it can help you.