  Membership inference attacks (MIAs) against machine learning models can lead
to serious privacy risks for the training dataset used in the model training.
In this paper, we propose a novel and effective Neuron-Guided Defense method
named NeuGuard against membership inference attacks (MIAs). We identify a key
weakness in existing defense mechanisms against MIAs wherein they cannot
simultaneously defend against two commonly used neural network based MIAs,
indicating that these two attacks should be separately evaluated to assure the
defense effectiveness. We propose NeuGuard, a new defense approach that jointly
controls the output and inner neurons' activation with the object to guide the
model output of training set and testing set to have close distributions.
NeuGuard consists of class-wise variance minimization targeting restricting the
final output neurons and layer-wise balanced output control aiming to constrain
the inner neurons in each layer. We evaluate NeuGuard and compare it with
state-of-the-art defenses against two neural network based MIAs, five strongest
metric based MIAs including the newly proposed label-only MIA on three
benchmark datasets. Results show that NeuGuard outperforms the state-of-the-art
defenses by offering much improved utility-privacy trade-off, generality, and
overhead.
