Machine learning plays an increasingly significant role in the building of Network Intrusion Detection Systems. However, machine learning models trained with imbalanced cybersecurity data cannot recognize minority data, hence attacks, effectively. One way to address this issue is to use resampling, which adjusts the ratio between the different classes, making the data more balanced. This research looks at resampling’s influence on the performance of Artificial Neural Network multi-class classifiers. The resampling methods, random undersampling, random oversampling, random undersampling and random oversampling, random undersampling with Synthetic Minority Oversampling Technique, and random undersampling with Adaptive Synthetic Sampling Method were used on benchmark Cybersecurity datasets, KDD99, UNSW-NB15, UNSW-NB17 and UNSW-NB18. Macro precision, macro recall, macro F1-score were used to evaluate the results. The patterns found were: First, oversampling increases the training time and undersampling decreases the training time; second, if the data is extremely imbalanced, both oversampling and undersampling increase recall significantly; third, if the data is not extremely imbalanced, resampling will not have much of an impact; fourth, with resampling, mostly oversampling, more of the minority data (attacks) were detected.