In the last week I have begun getting literally thousand of 'undeliverable message' emails on one of my machines. In looking at the header information it appears that the email account is being used to send out pornographic spam. The system has had up to date virus software and definitions and a firewall reunning all the time. When doing a virus scan the machine shows no infection and when running a spyware search I am finding very few bugs. When monitoring the machine I am showing no out of the ordinary activity, and there are no unusual services or apps running.
Is this a characteristic of a virus that has possibly disabled the virus software or is the email account possibly being spoofed by a spammer?
Thanks in advance for your assistance