A university is investigating after mistakenly sharing the personal details of about 2,000 students in an email promoting a lecture.
The email from the Creative Arts school at the University of Hertfordshire included an attachment with the recipients' names and email addresses.
The university said it had contacted the data protection watchdog, the Information Commissioner's Office.
It added that it took data protection "extremely seriously".
"The email was not sent to all students and the incident affected a group of students in one of our schools of study," it said.
"The relevant students were contacted immediately and the email was recalled.
"We are contacting all affected students with information and advice. We are carrying out an internal investigation and have informed the Information Commissioner's Office."
The email, sent on Wednesday morning, informed students about a fine art talk that afternoon with visiting artist Harold Offeh.