Is this a Virus?

So I have Webroot installed on my computer i bought in March. I just received in my outlook on one of my email addresses 10 emails with MAIL Undelievered to people i know i didnt send emails to! I looked at the send messages and all that was in there were LINKS. I immediately changed my password for email. But do i have a virus now? My computer has been runnin slower and freezing up. I thought WEBROOT would protect me from viruses? How do i find out if i have one this Webroot gave me no messages that i did?! I dont know much about that stuff
 
Any help appreciated.