From the 'I don't remember making an appointment with a spammer' files:

I get a lot of email over the course of any given day/week/month. I also tend to book many appointments for briefings and such (often driven by email calendar event requests). For the most part the only reason why my calendar is full is my own doing -- but there is a new risk that I've recently become aware of.

Calendar SPAM.

Yuup. Spam has evolved from just jamming your inbox to also polluting your Calendar too.  The Calendar spam technique targets both Microsoft Outlook and Google Calendar users. Security vendor McAfee recently blogged that they've now seen Calendar Spam too.

According to McAfee it's still a low volume threat. Apparently the way it works is by taking advantage of users who automatically accept incoming meetings (so just disable that if you're got it enabled) and then including the spam message in the event meeting details.

Sure it's something that can be easily avoided with some filters and proper configuration, but still it's something that's annoying. After all who want to get a Reminder popup letting them know they've got an appointment with Spam (unless it's the lunch meat and you put that into your calendar as a reminder of what you're going to eat...).