This has been going around with a ~500KB attachment:
Dear Mt.Gox user,
Our database has been compromised, how you already know.
To protect your account in the future, please download the Certificate (self-extracting archive) from Attachment and install it.
If you were using the same password on Mt.Gox and other places (email, mybitcoin.com, etc),
you should change this password as soon as possible.
Please accept our apologies for the troubles caused, and be certain we will do
everything we can to keep the funds entrusted with us as secure as possible.
Any unauthorized access done to any account you own (email, mtgox, etc) should
be reported to the appropriate authorities in your country.
The Mt.Gox team
Expect to see more like this if your email was leaked. It may be prudent to give up your email address as the spam will likely never stop.