1% to 5% of messages are lost entirely, even during normal operation conditions, and others may not be delivered until long after their relevance has passed. The use of SMS as an emergency notification service in particular has been questioned. Vulnerabilities The Global Service for Mobile communications (GSM), with the greatest worldwide number of users, succumbs to several security vulnerabilities. In the GSM, only the airway traffic between the Mobile Station (MS) and the Base Transceiver Station (BTS) is optionally encrypted with a weak and broken stream cipher (A5/1 or A5/2). The authentication is unilateral and also vulnerable. There are also many other security vulnerabilities and shortcomings. Such vulnerabilities are inherent to SMS as one of the superior and well-tried services with a global availability in the GSM networks. SMS messaging has some extra security vulnerabilities due to its store-and-forward feature, and the problem of fake SMS that can be conducted via the Internet. When a user is roaming, SMS content passes through different networks, perhaps including the Internet, and is exposed to various vulnerabilities and attacks. Another concern arises when an adversary gets access to a phone and reads the previous unprotected messages. In October 2005, researchers from Pennsylvania State University published an analysis of vulnerabilities in SMS-capable cellular networks. The researchers speculated that attackers might exploit the open functionality of these networks to disrupt them or cause them to fail, possibly on a nationwide scale. SMS spoofing The GSM industry has identified a number of potential fraud attacks on mobile operators that can be delivered via abuse of SMS messaging services. The most serious threat is SMS Spoofing, which occurs when a fraudster manipulates address information in order to impersonate a user that has roamed onto a foreign network and is submitting messages to the home network. Frequently, these messages are addressed to destinations outside the home network—with the home SMSC essentially being "hijacked" to send messages into other networks. The only sure way of detecting and blocking spoofed messages is to screen incoming mobile-originated messages to verify that the sender is a valid subscriber and that the message is coming from a valid and correct location. This can be implemented by adding an intelligent routing function to the network that can query originating subscriber details from the home location register (HLR) before the message is submitted for delivery. This kind of intelligent routing function is beyond the