SAN FRANCISCO (CBS SF/AP) — University of California and Stanford officials have confirmed that they were among the universities nationwide that have been targeted by a massive cyber ransomware attack.

The cybersecurity attack targeted a vulnerability in Accellion, a third-party vendor that is used to securely transfer files.

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“We understand those behind this attack have published online screenshots of personal information, and we will notify members of the UC community if we believe their data was leaked in this manner,” UC officials said.

In a statement, Stanford officials said its school of medicine school was targeted.

“Stanford University School of Medicine has learned that cyber criminals have claimed they have stolen some School of Medicine data as part of a cyber incident affecting a third-party file-sharing service, called File Transfer Appliance (FTA), provided by Accellion Inc. The breach was part of a larger national cyberattack on universities and organizations that use the Accellion FTA.”

“We are investigating this incident and we have reported the incident to law enforcement. We are working to determine whether individuals’ personal data has been affected, and we will notify any affected individuals.”

The hacker or hackers also have been sending threatening mass emails threatening to publish data “in an attempt to scare people into giving them money,” the UC statement added.

In an update Friday, the university system said the cyberattack affected about 300 organizations, “including universities, government institutions and private companies.”

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Other schools including Yeshiva University in New York City have reported that student and employee Social Security numbers and financial information were stolen and that some were posted online.

The information was obtained in December and January when hackers exploited a vulnerability in a 20-year-old Accellion file transfer service, various reports have said. However, some organizations said they only recently became aware of the breach.

The Baltimore Sun on Thursday reported that private information of staff members and students at the University of Maryland, Baltimore was posted online this week. The school said a hacking group known as Clop gained access to Accellion in December, the Sun said.

The University of Colorado and the University of Miami reported that files were accessed in January and included personal data and some health, study and research data.

The Washington State Auditor’s Office reported last month that information on nearly 1.5 million unemployment applicants had been stolen.

Accellion released a statement in March that said it had closed “all known” vulnerabilities and no new ones had been found.

Ransomware attacks on a massive scale and seeking massive payouts have hit several organizations in recent months.

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In an unrelated attack, the computer system of one of the nation’s largest school districts was hacked by a criminal gang that encrypted district data and demanded $40 million in ransom or it would erase the files and post students’ and employees’ personal information online. Broward County Public Schools, based in Fort Lauderdale, said in a statement Thursday that there is no indication that any personal information has been stolen and that it made no extortion payment to the ransomware gang.