mutable, though we limit the perturbations to changes that increase the initial values. The rationale behind such decision is that these fields, such as $src\_bytes$, can increase without altering the functionality of the traffic (e.g. null packets can be inserted). Decreasing these fields without expert knowledge of the traffic content would not be certifiably feasible. Other constraints on perturbations to the data are fields that are binary (the value can only be flipped from $0$ to $1$ and vice versa) and fields that are linearly related such as $same\_srv\_rate$ and $diff\_srv\_rate$ must sum to 1. A change to one of these fields alters the content of the other. Our analysis of the engineered features results in 93 immutable features and 29 mutable ones.

### UNSW-NB15 Data Set

The UNSW-NB15 data set was generated at the Cyber Range Lab of the Australian Centre for Cyber Security. It contains over 175,000 training samples and 82,000+ test samples that are labeled as benign or malicious (including attack type). The data contains nine types of more modern, low footprint attacks as described in [@7348942]. The benign traffic is more reflective of current network traffic as well. In this set, attacks compromise a much smaller 