The devastating WannaCry computer virus that broke out last year claimed a belated victim on Thursday as the cyber security company Sophos admitted it could not match the sales boom that had followed the security scare.

The London-listed company’s shares fell by more than a fifth as it said billings growth - an indicator of future revenues - in the three months to the end of June had slowed to just 6pc, or 2pc when adjusted for foreign currency changes.

The flatlining came in stark contrast to the years of repeated sales growth the company has enjoyed since its listing three years ago on the back of a booming cyber security industry.

On Thursday it said the WannaCry ransomware outbreak of 14 months ago, which crippled many NHS computer systems and forced companies to beef up their cyber security defences, had created a “particularly challenging comparable” that led to its growth stalling during its fiscal first quarter.

Investors had expected sales growth to slow, but not to the extent that Sophos revealed. In mid-May it had told shareholders to expect growth in the “high single-digits”, and Thursday’s unscheduled trading update was triggered only after crunching the worse-than-expected figures.