Snape read the decrees with interest, though they weren't surprising. The news that Dumbledore and Order of the Phoenix had been Tabooed brought a sneer of utter contempt to his face. Could Riddle make his fears any more obvious? Moron.
The news that Portkeys, Apparation and Floo travel and calls were monitored wiped the smirk off Snape's face. Hm. Perhaps not entirely moronic after all.
Though he had to agree with Theo's assessment of the perils of mail. The Serpenscript charm would be too difficult to teach by any other means than in person; it would have to be the Patronus.
He picked up a tightly rolled scroll of black parchment, cast Serpenscript, and spoke, knowing that his voice would only be audible to Theo, and that the message could not be tampered with, without being destroyed.
"Mr. Nott,
I appreciate the update, and agree with you on the inadvisability of written communication.
To that end, I wish you to learn two new charms. The first is the Patronus charm; it conjures an ethereal animal which is unique to the caster. The caster must concentrate solely on an extremely happy memory while incanting 'Expecto patronum'.
When you have achieved a fully corporeal Patronus - instead of the wisp of silver light which is its precursor - you should then learn the second charm, which allows you to use the Patronus as a courier for messages that cannot be intercepted or falsified by Dark magic. Gaze into your Patronus' eyes, reach out to it with your mind, and incant 'Animalocutio'. Then touch your wandtip to your lips then move it eastward in a triple widdershins spiral. After the gesture is complete, speak your message, then the name of the recipient. Your Patronus will find that person no matter where they are, and repeat that spoken message, in your voice, to that person and none other.
I look forward to hearing of your success in learning these charms, from your Patronus.