I received this from a friend but 'knew it wasn't really from him. What this scam is designed to do is, gain access to your contacts list, and send the same eMail to all of them. It will show up as FROM YOU! These people are harvesting millions of eMail address to bundle and sell to unscrupulous scammers.
Please take this seriously. If you have clicked on one of these, change your password immediately.
For more information on how to revoke permissions you have unknowingly granted, see the following brief article: https://support.google.com/accounts/answer/3466521?hl=en