Mobile devices such as smartphones and tablet PCs are increasingly used for business purposes. However, the trustworthiness of operating systems and apps is controversial. They can constitute a threat to corporate networks and infrastructures, if they are not audited or monitored. The concept of port-based authentication using IEEE 802.1x restricts access and may provide statistical data about users entering or leaving a network, but it does not consider the threat that devices can pose when already authenticated and used. Mobile devices gather and publish information. This information is incorporated into Security Information and Event Management (SIEM) software so that a threat is recognized while the device is being used.