I'm pretty sure this subject was discussed many times, but can't find an answer for it.
A new service has appeared in Poland, which enables users to exchange text links. A user is theoretically able to choose which websites can advertise on the user's website, but practically most users choose any website.
I have two questions:
Is it OK from Google's TOS's point of view?
And - how actually Google detects it? If the ads are printed by a php script with simple links, how can google detect it?