How did Bitfinex hack work?

Could you elaborate on the mechanics of the Bitfinex hack? Specifically, how did the perpetrators gain access to the system, what vulnerabilities were exploited, and how did they manage to execute such a large-scale theft of funds? Additionally, what measures were in place at the time of the hack to prevent such an incident from occurring, and how has Bitfinex since strengthened its security protocols to prevent future breaches?