At least half the advert visible for one continuous second, measured on our own servers. Anything less is not billed and not deducted from your block.

No. There is no user data to target with. You choose topics and properties; readers choose the topics they will accept. That is the entire targeting model, and it is why there is nothing to leak.

You get 110% of the shortfall added to your block at no charge. Blocks do not expire, so a slow month costs you nothing.

Neither. One published rate, prepaid in blocks, sold directly by the company that owns the properties. Founding advertisers keep today’s rate for 24 months.