1. A communications security system to prevent transfer of selected communication transactions from an untrustworthy network to a trustworthy network, comprising: a server, connected to the untrustworthy network, that maintains a database of protection rules, each of which, when applied to a communication transaction, identifies that communication transaction to be a respective one of the selected communication transactions; and a portal, connected between the untrustworthy network and the trusted network, that: selectively transfers the database of protection rules from said server via said untrustworthy network; receives a communication transaction from the untrustworthy network for transfer to the trustworthy network; applies each of the protection rules to the received communication transaction; and prevents the transfer of the received communication transaction to the trustworthy network if a protection rule identifies the received communication transaction to be a respective one of the selected communication transactions.