Dyn-Backdoor: Backdoor Attack on Dynamic Link Prediction
  Dynamic link prediction (DLP) makes graph prediction based on historical
information. Since most DLP methods are highly dependent on the training data
to achieve satisfying prediction performance, the quality of the training data
is crucial. Backdoor attacks induce the DLP methods to make wrong prediction by
the malicious training data, i.e., generating a subgraph sequence as the
trigger and embedding it to the training data. However, the vulnerability of
DLP toward backdoor attacks has not been studied yet. To address the issue, we
propose a novel backdoor attack framework on DLP, denoted as Dyn-Backdoor.
Specifically, Dyn-Backdoor generates diverse initial-triggers by a generative
adversarial network (GAN). Then partial links of the initial-triggers are
selected to form a trigger set, according to the gradient information of the
attack discriminator in the GAN, so as to reduce the size of triggers and
improve the concealment of the attack. Experimental results show that
Dyn-Backdoor launches successful backdoor attacks on the state-of-the-art DLP
models with success rate more than 90%. Additionally, we conduct a possible
defense against Dyn-Backdoor to testify its resistance in defensive settings,
highlighting the needs of defenses for backdoor attacks on DLP.
