How many times has Kraken been hacked?

Excuse me, I'm quite interested in the security of cryptocurrency exchanges. As a professional in this field, I'm sure you're aware of the recent hacks that have occurred on various exchanges. Specifically, I'm wondering about the security record of Kraken. How many times has Kraken been hacked in the past? And if so, what measures have they taken to prevent future attacks? I understand that no system is completely secure, but it's important to know how exchanges like Kraken respond to these challenges and protect their users' funds. Thank you for your time and expertise.