Yes and our worrying about SETI security is akin to Romans wondering how we might exploit a weakness in the Caesar Cipher to invade them. If we have B2 Bombers and bad intentions, then surely we don't need to exploit any of their systems to inflict damage. A sufficiently advanced alien race, intent on destroying us, is not going to give up because we shut down SETI. Why would they want to use such a primitive technology as their means of attack to begin with?