stop the spam from google groups

when you received an invitation from google groups, and
you  think it is a spam..

Just press 'CTRL+END' to the bottom of the mail, and you can find a
report URL to Google..

Wait and see if this behavior works...

BTW, when you received the spam from Yahoo..
The best method to stop it is block the whole content from '@YAHOO.com' & '@YAHOOgroups.com'..
Stupid but effective...