This issue exists because [this line](https://github.com/BorealisAI/advertorch/blob/master/advertorch/attacks/fast_adaptive_boundary.py#L22-23): `from advertorch.attacks.utils import zero_gradients` which refers to the `zero_gradients` function in PyTorch is obsolete. This is because `zero_gradients` is [removed](https://github.com/pytorch/pytorch/blob/master/torch/autograd/gradcheck.py) from PyTorch 1.9. It was [present](https://github.com/pytorch/pytorch/blob/1.7/torch/autograd/gradcheck.py#L10) until PyTorch 1.7.