Are your friends getting Spam from your email address?
You’re Email has been Hijacked.
To fix this you can try two tactics:
1. change your password, or
2. abandon your email address – get a new one and email all your friends from the new email address.
Before you do either you should run two cleaning programs – anti-virus (like Avira) and a Spyware cleaner (like Spybot)
For the expert – click here for more advanced info