A new virus?

hello,

I do not normal post on here. I have just been hit by my first virus which I am finding very odd. I just opened my hotmail account for the second time today and I have found my hotmail has sent out an email to everyone on my email address book an email with the subject line Opa. I do not know how my computer has got infected or got hijacked. I never open emails from people I do not know I do not open emails that contain attachments from people I dont know. I have an up to date Nortons. Is this a new virus as I cannot see it on the virus definitions list on this site or any others? If it isnt how to do I get rid of it?

Thank you,