Downloading from Internet

I have no active applications that need to download from the internet, however there is constant traffic being downloaded.

the only active programs are those required by Windows XP Pro. I have switched off Automatic updates for Windows and Avast.

I have the latest updates for both. I did a scan but no viruses were found.

I use a Celluar connection for Internet access. I have swopped with another user, the problem is only on the one pc.

I suspect a virus/malware, but as Avast does not find anything Iā€™m a bit lost.

any ideas?

I suggest you use a two-side (inbound and outbound) firewall:

Online Armour
PCTools
Outpost Firewall Free
Comodo
ZoneAlarm

Personal Firewall Tests & Results. Firewall rating:
http://www.matousec.com/projects/firewall-challenge/results.php
About the leak tests limitations: http://forum.avast.com/index.php?topic=29259.msg247460#msg247460

Freeware firewalls:
http://www.firewallleaktester.com/tests_overview.php
http://www.thefreecountry.com/security/firewalls.shtml

Also, you can use TCPView for Windows v2.54 to know what is running into Internet
http://technet.microsoft.com/en-us/sysinternals/bb897437.aspx

Thx, will try it

You can upload the files that want to use the internet to VirusTotal to see if its a virus or not.