Our official privacy policy has yet to be written. Until then, here's essentially what we do.
Messages posted on the TCS bulletin board are in one of two forms: public or private. Public messages that you post can be read by any TCS member. Private messages that you post can be read by yourself, by the recipient that you name while posting the message, and by any of a number of system operators who keep an eye on the boards and make sure they remain civil. For a greater degree of privacy, contact each other via e-mail.
We maintain online order forms at the request of many of our overseas and local members. These are not secure order forms like you'll find at most e-commerce sites. They are simply a convenient way to get order information to the Pi's office manager. If you aren't comfortable submitting payment information over the Web or by e-mail, you're welcome to print out the forms and mail them in, or to contact the office during our business hours.
No Internet e-mail system is completely private. Don't ever write anything online that you don't want read back to you at your hearing.