This paper studies the user-level security of mobile systems. The current mobile phone users trust the invisible security of the 2G systems. The evolution from the second-generation mobile systems (2G) to the third generation systems (3G) will introduce the threats and opportunities of the Internet to the world of mobile communications. From the technical point of view, the new security requirements are similar to the security requirements met with today in a company Intranet environment. There is, however, one great difference; the charge paid for accessing the service. In future the users of mobile systems will have to be more aware of the security issues.