This is very common at the moment but Please don't post the link in future - Forum Members are warned not to follow the link in the original post!!!
If you are receiving these from people in your address book as individuals it is probably their e-mails that have been hacked. If you are receiving mailer-daemon for messages that you have apparently sent to undeliverable e-mail addresses it's your e-mail that has been hacked. Changing passwords is the first step in either case. It is important not to use "dictionary" words or names and numbers - these are cracked very easily. Add in "Wild Card" symbols such as @ for a, zero for o, $ for s even ^,%,* etc.
When people send round robin e-mails or pass on chain mail with recipients clearly visible in the To or CC fields, every one of those addresses becomes a target for hackers and can be harvested for this type of spamming. Hackers will then try to log into those e-mails using webmail and use password cracking software using dictionery word and letter combinations to access that account and then harvest every contact.