The expiration of a key digital encryption service on Thursday sent major tech companies nationwide scrambling to deal with internet outages that affected millions of online users.

Tech giants — such as Amazon, Google, Microsoft, and Cisco, as well as many smaller tech companies — were still battling with an endless array of issues by the end of the night. The problems were caused by the forced expiration of a popular digital certificate that encrypts and protects the connection between devices and websites on the internet. The certificate is issued by Let’s Encrypt, the largest issuer of such certificates in the world.