Cub is one of many grocers in the Twin Cities and nationwide caught in the fallout from a cyberattack on its parent company, wholesale distributer UNFI.

For the grocery stores and co-ops that rely on UNFI for food shipments — including Whole Foods, Kowalski's and Lunds & Byerlys locally — that means potentially empty shelves after no-show deliveries. Specifically at Stillwater-based Cub, half of the pharmacies in its stores are offline as UNFI works to resolve the hack to its IT systems discovered just this past Thursday.

Cub, which UNFI bought in 2018 as part of its SuperValu acquisition, has "proactively taken certain systems offline, which has disabled systems" at some of its pharmacies, the company posted to its website Tuesday.

"At pharmacies still experiencing the disruption, we are unable to fill new and refill prescription orders at this time," the statement read.

Signs posted at the St. Louis Park Knollwood Cub pharmacy on Tuesday afternoon read: "Technical difficulties! Our phones and our prescription system are down."

Rhode Island-based UNFI delivers food to more than 30,000 locations across the United States and Canada, including both national and local grocery chains. Kowalski's and Lunds & Byerlys were not immediately reachable Tuesday evening.

Whole Foods told Reuters the grocery chain is working to restock its shelves "as quickly as possible."

UNFI, which has $31 billion in annual revenue, disclosed this week "unauthorized activity" had occurred in its systems last Thursday but offered few other details around the nature of the cyberattack. UNFI was also mum on the extent of the impact to its food deliveries.

The company, which has a major distribution center in Hopkins, is shipping to customers "on a limited basis," UNFI Chief Executive Sandy Douglas told analysts on a conference call Tuesday morning.

"We have implemented workarounds for certain operations in order to continue servicing our customers where possible, and we're continuing to safely bring our systems back online and restore broad-based customer service as soon as possible," he said.

UNFI said it aimed to bring its systems back online by Sunday, according to an email to customers Bloomberg reported. The outlet also reported warehouse workers were resorting to pen and paper to track orders.

Local Teamsters officials did not answer a question Tuesday about the impact on their 850 members who work for UNFI in Hopkins.

Analysts pressed for more details on Tuesday's call, but Douglas wouldn't offer estimates on costs or the number of stores or routes affected. This while anecdotal reports bubbled on social media of grocery stores not receiving shipments to restock shelves and UNFI drivers not making deliveries because of the system shutdown.

"We're 100 hours in. At this stage, we are taking action with two tracks of focus," he said. "The first is to address the cyber incident to make sure we understand it, that we've taken actions to repair, improve. And then get our system safely online as fast as possible."

Cybersecurity expert Ferhat Dikbiyik wrote in an email the scale of the disruption has the hallmarks of a ransomware attack: hackers holding up systems and demanding payment. He said, however, the repercussions of the attack could go far beyond potentially compromised data.

"The food supply chain depends on movement," he wrote. "When that movement stops, nothing else matters. Warehouses freeze. Routes break. Perishables don't wait."

Cub pharmacy customers who had their prescriptions filled before Friday can still pick those up, the company said.

For others: "We recommend filling them at another local pharmacy retailer. We are continuing to work to restore our systems to safely bring them back online."