First, never use any kind of "anti-virus" or "anti-malware" software on a Mac. That's how you cause problems, not how you solve them. Your problem is certainly not caused by a "virus."
Most likely, a spammer has compromised the mail account or PC of one of your contacts, and is forging your address as the return address in the headers of his messages. The bounce messages from mail servers that reject the spam come back to you. You should check your own mail accounts to make sure there's been no unauthorized activity.
You can create a Mail rule to delete the bounce messages automatically. Most often, the problem lasts only a few days before the spammer moves on to another forged address.