Much discussion is occurring about the security of the tunnel established
between the client and the server. Bruce Schneier, president of the
cryptographic consulting firm Counterpane Systems and author of Applied
Cryptography (John Wiley & Sons), has raised serious concerns about the
security of Microsoft's implementation of the Point-to-Point Tunneling Protocol (PPTP). You can find information about Counterpane Systems' cracking of PPTP at http://www.counterpane.com/pptp.html. You can find Microsoft's response to Counterpane Systems' concerns at http://www.microsoft.com/ntserver/basics/communications/ basics/securevpn/default.asp.