The purpose of the NGMN 5G security group, which is a sub-group of the NGMN P1 5G Architecture group, is to identify new threats and security issues that may arise with 5G. The work of the group aims at informing the 5G community, and especially SDOs (like 3GPP) of potential problems in 5G, what we should pay attention to. This working group does not make requirements, just recommendation that people should have in mind when designing 5G networks. The group will release several documents with different focus; this first package focuses on Improving the Access Network and also identifies DoS attacks scenarios in a 5G context. Some of the identified threats are not specific to 5G but will be emphasized in a 5G context, and thus should be very carefully considered when designing the 5G networks. Some of the recommendations described in this document might also be applicable to the current generation mobile networks.