Tech blogger Amit Agarwal has been receiving suspicious, spam-like alerts from his Google Calendar lately reminding him to collect millions from an ATM, among other things. If you've seen similar GCal spam, your first instinct may be that your account has been hacked. On the contrary, clever spammers are taking advantage of a Google Calendar feature that automatically adds events to your calendar as soon as you're invited—which means all a spammer needs to do is send his spam via GCal's Add Guests feature. To fix this, head to your GCal settings and find the entry labelled, "Automatically add invitations to my calendar," then switch from the default (Yes) to "No, only show invitations to which I have responded." Google should probably switch the default to No, but in the meantime, this tweak will do the trick.