email bounce backs

[#1]

Hi
Overnight I've had over 300 bounce back emails into my mailbox.  I assume that my user name has been cloned to send spam, and so I'm getting the failures.  Is this happening to anyone else at the moment?
John

[#2]

normally a diferent person each day, about four others complained recently about back scatter

[#3]

Thanks Pierre.  I usually get a few, but this morning was really bad.
John