They don’t yet know the extent of the hack and exactly which of their customers are affected. But if you’ve made a purchase at any of their gas stations, coffee shops or restaurants then you could be impacted. They also didn’t indicate how long this has been going on for.
Here’s their official announcement:
https://www.hy-vee.com/corporate/news-events/announcements/notice-of-payment-card-data-incident/