BUFFALO, N.Y. (AP) — An unknown number of students taking the statewide English assessment by computer encountered delays when a security feature in the system "inadvertently activated" and prevented them from logging in, New York education officials said on Thursday.

The problem on Wednesday originated with test vendor Questar Assessment Inc., which eventually fixed the issue, Education Department spokeswoman Emily DeSantis said.

Testing continued on Thursday without any additional interruptions.

"We are requiring that Questar perform a root-cause analysis and develop a corrective action plan to ensure a similar issue does not occur again," DeSantis said.

The department said it does not know how many students were affected because the testing system does not capture log-in attempts. About 50,000 students completed tests on Thursday.

Minnesota-based Questar did not respond to a request for comment. The company was hired by the state in 2015 under a five-year, $44 million contract to develop and administer English language arts and math assessments given annually to students in grades three through eight.

The state began transitioning from paper- to computer-based testing in 2016 and is expected to test all students by computer in 2020. About 260 of the state's more than 700 districts used computer-based testing this week. Nearly 1 million New York students are eligible for the annual English language arts assessment, as well as math testing scheduled for next month.

The state's teachers union said Wednesday's problems raised questions about the plans to use computers for the tests, which have been the subject of protests in recent years. Intended to measure student and school progress, critics see the assessments as unfair and unnecessary demands on classroom time.

New York State United Teachers said the union was flooded on Wednesday with reports of system crashes and log-in failures from teachers in Victor, Saranac Lake and elsewhere.

"If (the state Education Department) wants to restore the trust and confidence of parents in its testing system, this isn't the way to do it," NYSUT Executive Vice President Jolene DiBrango said.

On Wednesday night, the state Education Department posted instructions on its website for recovering test responses that appeared to be lost when students were "booted out" of the testing system.

It was the second time this year that state officials found themselves answering questions about Questar. In January, a data breach exposed personal information of about 52 students in five New York schools, leading to an investigation by New York Attorney General Eric Schneiderman's office. The investigation is ongoing.

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