The cause of the downtime according to the response was caused by a script reading error when Salesforce was attempting to update their forms. As a result, those who used Salesforce Pardot was completely locked out of their databases as the vulnerability was exploitable by hackers. As a precaution, Salesforce had to shut down all of their servers and temporarily revoke admin privileges understandably upsetting many customers.[1]
The vulnerability showed how easily an interconnected program can destroy a business if not prepared. If it was a focused attack rather a coding error, Salesforce would be looking at millions in damages. Checking your scripts and patches regularly will keep issues like this from becoming full disasters.
[1] https://www.zdnet.com/article/faulty-database-script-brings-salesforce-to-its-knees/