As a web professional I can tell you that it's probably not the QB that has been hacked, but one or more of the individuals that the emails came from. They may have a virus or malware that is sending this garbage to any email addresses in their email program. You would be doing them a favor to let them know about the problem. If you don't want to email them (because you'll be exposing yourself to more spam) then you should PM them here on the board. I know I would appreciate the heads up. With this type of virus or malware it is very common for the individual to not know that it's coming from their computer.
I hate hackers, etc.!