A WebmasterWorld thread has several publishers complaining that when they checked their ad serving settings in their AdSense console, the VPAID ads were on by default. That means, your web site may show video ads to your users.
Many publishers dislike showing video ads, so it was upsetting for them to see this just on by default, as opposed to opt in. VPAID ads are described as:
Choose whether or not you want to display interactive VPAID video ads. VPAID is a standard that allows advertisers to create interactive video ads, e.g., overlays, galleries, etc. Note that this opt out does not apply to non-VPAID interactive video ads, e.g., TrueView video ads.
You can learn more about them on the IAB web site.
Here is the setting, which was on by default for me to under "Allow & block ads" > "Ad Serving".
Make sure you control the ad types you want on or off on your site.
Forum discussion at WebmasterWorld.