Keio is a leading research university where 33,436 students are currently registered with 3,140 faculty members. The university system was cracked in September 2020 by malicious crackers where it is composed of the internet-connected-integrated database across the administrative and academic units. The cracked system was completely down, so that all courses from October 1 to October 7 in 2020 were canceled except my courses. The minimum survival system using private mail servers functioned, and my online courses were successfully held. This article shows my story of how to build a resilient secured education system for online lectures against malicious attacks during the pandemic.