Omitting the "how much" isn't especially surprising for a transaction between private companies. But not saying who the counterparty is -- well, that just underlines how under-the-radar they want that business to be.
If Forbes really doesn't know where those ads are, they should talk to the folks who are in charge of digital revenue. Probably their digital bizdev folks.
And don't kid yourself. Forbes is *far* from the only big media property doing this.