Anti-PHORM campaigners point out that website owners own the copyright on the contents of their pages, and so can impose terms and conditions that selectively grant real human visitors and legitimate proxies the right to make copies of (ie fetch) their content, and can also withhold the granting of any such rights to evil computers such as those operating PHORM garbage. Such evil computers would then be carrying out acts of infringement. It is not the copyright holder's job to inform would be infringers of the copyright, quite the reverse, it's BT/Phorm that need to establish that they have been granted the right to copy pages from web servers unless they want to risk action being taken against them for infringement. Putting up a notice explicitly reminding PHORM or BT or similar that they are granted no such licence, or even writing to them to remind them of the law would put them in an impossible position if you detected an infringement in your server logs. That's the strategy that has been suggested anyway.
This is rather more subtle than simply not allowing them access at all, and should it is hoped give them or their legal depts nightmares if enough people started giving out such indications.
