TSMC, sole supplier of the A-series chips used in Apple’s iPhones and other devices, has admitted that the ultimate cause of its virus-induced downtime was the use of unpatched Windows systems …

The company initially said only that the problem, which resulted in several factory shutdowns, was caused by an unspecified computer virus. V3 reports that TSMC has since elaborated on this, admitting the embarrassing details.

WannaCry was a ransomware attack first seen back in May 2017, and was estimated to have attacked more than 200,000 PCs across 150 countries.

The company admitted the outbreak […] affected unpatched Windows 7 systems running critical processes in its fabrication facilities.

TSMC had absolutely no excuse for its systems remaining vulnerable more than a year later. Microsoft had actually issued patches prior to the main attack, and followed up with emergency patches within a few days. That the chipmaker hadn’t applied these, or later updates, on production-critical systems is astonishing.

While the company did quickly get its systems back online, it has estimated that lost production during the downtime will reduce its quarterly revenue by 3%, and analysts say that shipments of the new iPhones could be delayed as a result.