I've started getting spam recently from my wife's gmail account.
Obviously senders can easily spoof from addresses, but this is a bit more diconcerting; they obviously know that im on my wife's contact list (hence sending the spam to me), and also there's generally a few people from her contacts list cc'd on the mail.
This suggests that someone has got hold of her contacts list.
How worried should I be?
You shouldn't... Any chance your wife occasionally sends out mails with groups of people listed in the CC: field? Does she, you, or any of your contacts have links to the rest of you on a social networking site where email addresses can be seen? There are hundreds of ways groups of people can be tied together using publicly available information, or simply even one of her contact's machines all virused up and reporting email groups back to spammers...
This is assuming, of course, that she doesn't keep sensitive information in her contact list stored electronically. If you'd be nervous about printing it out and letting a restaurant full of people skimming over the information there, then yes, be worried.
There's always a possibility that her account has been compromised. She should change her password ASAP.
At the bottom of the page on Gmail there's also a link for "Last account activity" which will show all of the IP address that have been used to connect recently. If some of them are out of your general area you have a problem.
This is surely a compromise, and your wife should change her gmail password and anything related authentication ASAP.
