General Secretary Matthew McGowan told members yesterday afternoon that the union’s servers and networks had been “subject to a ransomware attack” overnight

“While at this early stage we cannot be certain of the extent of the data breach and its implications, the potential exists that your personal details may have been compromised,” he warned.

Mr McGowan urged members to change on-line banking and credit card passwords and to check for fraudulent or suspicious activity.

“As with many other organisations, all our precautions were unable to prevent this malicious attack,” he added.