Deleting the data after verification is a good practice. But if you're actively compromised, it probably doesn't matter how long you keep the data because it's already been immediately "backed up" by the intruders the second it is collected.

Much like Target and Home Depot with their big credit card breaches a decade ago. Everyone was up in arms about these companies "storing" full credit card records, when in reality the attackers had card-sniffing malware installed on every single cash register at every single store across the country.