Looks like iSkoot made a mistake with their Nokia S60 client and will make it right. Apparently a non-production version of the S60 client made it to the public web, which sends data in the clear. Other published versions of their client on other platforms are unaffected.
iSkoot CEO Mark Jacobstein says the existing S60 build will be pulled. The bug will be fixed and a forced upgrade to a patched version will be pushed.
Thanks to Andy Abramson and Jim Courtney for their behind-the-scenes help with this. Update: Forgot to thank Dan York as well, who helped despite spending the weekend driving a U-Haul. :)