I logged in to my gmail today, and saw it had sent spam mails to different people: "...I read this article and I'm tempted to do it myself... [Spam URL]"

I wonder if I have malware on my computer, or what is going on? The messages were sent to different mails, but didn't seem to get through, as I got mails in my inbox.

Should I change my password on my email, or try to remove the possible malicious content on my computer?