"We have been informed by Metro Hartford Information Services (MHIS), our City of Hartford shared services team that manages our network infrastructure, that the ransomware virus caused an outage of critical systems and the restoration of those systems are not complete," a notice from The Hartford Public Schools Team read.
The notice added that the attack also impacted the city's system that communicates bus routes to the company that transports Hartford students, which prevented schools' "ability to operate" on Tuesday.
Classes have been canceled for both in-person and online learning, according to local newspaper The Hartford Courant.
"Everyone at Hartford Public Schools was ready to welcome back our beautiful and capable students in person and remotely. We will provide updates when we have additional information to share," the notice said.
Hartford schools are using a hybrid learning model for the 2020-2021 school year amid the coronavirus pandemic, meaning students have the option to return to class full-time either in person or online, according to the school district's website.
Students in pre-K through second grade, sixth grade and ninth grade were supposed to start on Tuesday as part of the city's staggered reopening plan; grades three through five, as well as seven and eight, are expected to start Wednesday.
High schoolers will be split into two groups — the first of which will attend their first day of in-person learning on Thursday, and the second of which will begin in-person learning on Friday.
Hartford Public Schools has yet to announce whether the ransomware attack will impact its staggered reopening plan.
The city is requiring all public school students to wear masks and social distance while attending in-person classes; buildings will be sanitized daily, and buses will be cleaned after every trip, among other safety measures to prevent the spread of the virus, according to the school's "Return to Learn" manual.
Connecticut Gov. Ned Lamont in May announced $111 million in federal COVID-19 relief funding for the state's public schools.