Paracab,
I assume that your computer is directly connected to the BT ADSL device without any intervening firewall / router.
If you are, and are not running a personal firewall - e.g. BlackICE defender, ZoneAlarm or similar - your computer is completely open to the internet and to those who would abuse it.
Your computer may even now unwittingly be taking part in a spamming or denial-of-service attack as a "zombie", controlled by a remote computer hacker. It could be being used as a file server, the contents of which files you would not want to know.
For your protection and the protection of others with whom you exchange information, please get yourself a hardware or software firewall and an AV program with regular (at least monthly, preferably weekly) updates.
I use BlackIce with a Netgear firewall, together with Sophos, updated weekly - or sooner if I read of any new virus (OK, I'm lucky, I get Sophos through work). I also use AdAware and SpyBot.
Please forgive me if you have already implemented the above, I'm not having a go or accusing you or anything, just pointing out the dangers of permanent IP connection to the internet, and the responsibilities that go with the benefits and convenience of Broadband.
Safe surfing,
SD