Near Field Communication (NFC)-enabled mobile phones and services are starting to appear in the field, yet no attempt was made to analyze the security of NFC-enabled mobile phones. The situation is critical because NFC is mostly used in the area of payment and ticketing. This paper presents our approach to security testing of NFC-enabled mobile phones. Our approach takes into account not only the NFC-subsystem but also software components that can be controlled through the NFC-interface. Through our testing approach, we were able to identify a number of previously unknown vulnerabilities, some of which can be exploited for spoofing of tag content, an NFC-based worm, and for Denial-of-Service attacks. We further show that our findings can be applied to real world NFC-services.