Email Worm

Please help me... I have some kind of worm that has gotten into my laptop and sending itself to everyone in my email address book. I'm not very technically minded, but I'll try and give as much info as I can. Its a Dell Inspiron 1546 laptop. It runs Windows 7 and has Norton 360 V.4 installed, I also use Hotmail to send and recieve my emails. This is how things play out... I'll be busy with something on the laptop when MSN Messenger brings up 3 emails. 2 from the postmaster notification telling me that it is unable to deliver to 2 of my contacts and then another email from myself. At this point I haven't emailed anybody. Friends and family are also telling me that they are getting ccountless strange looking emails from me. This is normally happening about twice a week, but it has now happened twice in the last 12 hours. I've run a full Norton scans which have never picked up anything more than tracking cookies. Yesterday I had a very unhelpful Norton agent take control of the laptop so that they could use 'more powerful tools.' This also showed no viruses. After I had read a few internet articles I decided to download and run Malwarebytes, but this also showed nothing. Having checked my email this morning to find more post master notifications and more emails from myself a friend suggested that I try here in the hope that someone may be able to help.