When universities went online in response to the coronavirus pandemic, so did the tests their students took. But one of the people who logged on to take an exam in a pre-med chemistry class at a well-known Mid-Atlantic university turned out not to be a student at all.

He was a plant. An impostor. A paid ringer.

Proctors — remote monitors some schools have hired to watch test-takers through their webcams — discovered by reviewing video recordings that this same person had taken tests for at least a dozen students enrolled at seven universities across the country.

But he was in Qatar, beyond the reach of any attempts to hold him accountable, according to proctors familiar with the situation. They could not say what happened to the students who allegedly hired him.

It was a dramatic case but far from unique. Universal online testing has created a documented increase in cheating, often because universities, colleges and testing companies were unprepared for the scale of the transformation or unable or unwilling to pay for safeguards, according to faculty members and testing experts.

Even with trained proctors watching test-takers and checking their IDs, cheating is up. Before the coronavirus forced millions of students online, one of the companies that provides that service, ProctorU, caught people cheating on fewer than 1 percent of the 340,000 exams it administered from January through March. During the height of remote testing, the company says, the number of exams it supervised jumped to 1.3 million from April through June, and the cheating rate rose above 8 percent.

“We can only imagine what the rate of inappropriate testing activity is when no one is watching,” said Scott McFarland, chief executive of ProctorU.

And for most online test-takers, no one has been watching. One reason is that, as demand for online testing spiked, proctoring capacity was overwhelmed. One company, Examity, suspended its live proctoring services during the demand surge when its 1,000 proctors in India were locked down to curb the spread of the coronavirus there. Ninety-three percent of instructors think students are more likely to cheat online than in person, according to a survey conducted in May by the publishing and digital education company Wiley. Only a third said they were using some type of proctoring to prevent it. Many colleges and universities moved ahead with online testing without supervision to save money. Others opted instead for less expensive, scaled-down kinds of test security, such as software that can lock a web browser while a student takes a test.

While locking a browser during an exam may help — and about 15 percent of instructors take that step, the Wiley survey found — it can’t stop other forms of cheating.

“You cannot give an exam if it is not proctored,” said Charles M. Krousgrill, a professor of engineering at Purdue University, where faculty have been more willing to publicly discuss cheating than their counterparts at many other schools.

When, after the coronavirus shutdowns, Purdue gave students extra time to take their tests online, said Krousgrill, “there was rampant dishonesty.” He described some students in his department organizing videoconferences and sharing answers. “Once we went to online instruction, we could not watch. [The students] knew it and knew the game was up for grabs.”

Online tests have also meant a booming business for companies that sell homework and test answers, including Chegg and Course Hero. Students pay subscription fees to get answers to questions on tests or copies of entire tests with answers already provided. The tests are uploaded by other students who have already taken them, in exchange for credits, or answers are quickly provided by “tutors” who work for the sites.

Though these sites have been around since before the pandemic, their use appears to have exploded as more tests are given online. Students used Chegg to allegedly cheat on online exams and tests in the spring at schools including Georgia Tech, Boston University, North Carolina State and Purdue, according to faculty at those institutions and news reports.

At North Carolina State, more than 200 of the 800 students in a single Statistics 311 class were referred for disciplinary action for using “tutor-provided solutions” to exam questions from Chegg, said Tyler Johnson, the course coordinator.

After the exam, Johnson said, he asked his university to get Chegg to remove the questions, citing copyright law. Chegg did, and it furnished a report of users who had either posted or accessed the exam materials.

“I was initially really naive to the extent to which these services are utilized by students,” he said.

The North Carolina State students have protested in a petition that they didn’t know using Chegg would be considered cheating and that Johnson showed “no regard to the personal stresses we are enduring and have endured throughout the semester.”

Krousgrill and his colleagues at Purdue found “a massive number” of students who had used Chegg to get test answers, he said. In one class, Krousgrill said, as many as 60 students out of 250 had done so, and 100 students in a colleague’s class were identified as having used Chegg in a similar fashion.

The number of students who are cheating is almost certainly higher than the number being caught or reported. Research has shown that instructors believe cheating happens much less often than students do, which means they may not be looking for it. When they do find it, many choose to simply give cheaters an F, without reporting the incidents further.

“I had a conversation with a group of students several months ago,” said James Pitarresi, vice provost at Binghamton University. “And one of the students said, ‘Look, you know, probably 80 percent of the class is looking at Chegg. What are you going to do, expel all of us?’ ”

Chegg, which offers online tutoring services, declined to comment at length. A spokesman said the company supports academic integrity and hasn’t seen “any relative increase in honor code issues since the covid-19 crisis began.” In an interview with the New York Times, Chegg chief executive Dan Rosensweig, when asked whether his company’s services were being used for cheating, said: “Let’s face it: Students have always found a way, whether it’s in fraternities, or whether they go to Google. But Chegg is not built for that.”

The firm reported $153 million in revenue for the second quarter, when the pandemic shutdowns were at their peak — a 63 percent year-over-year increase.

Colleges were not the only institutions to rush examinations online. Advanced placement and other tests also went virtual in the spring. So did law school entrance and placement exams, professional certification tests for financial managers and food handlers and many others.

The College Board, which administers the AP tests, reconfigured these exams to be “open book” when they were moved online, but without proctoring. Students reportedly used private messaging apps to collaborate on answers. Even before the exams began, College Board officials tweeted about “a ring of students who were developing plans to cheat” and canceled their registrations.

The College Board won’t disclose whether any cheating actually happened. A spokesman would say only that “at-home testing presents some different security challenges” and that the organization took steps to prevent it.

“One student with a pattern of cheating is an ethical problem for that student. Multiple students with a pattern of cheating devalues any grade or degree they might be receiving,” said Steve Saladin, a co-author of a study published in the spring by the Journal of the National College Testing Association. “And when cheating spreads to many students in many programs and schools, degrees and grades cease to provide a measure of an individual’s preparedness for a profession or position. And perhaps even more importantly, it suggests a society that blindly accepts any means to an end as a given.”

This story about online testing was produced by the Hechinger Report, a nonprofit, independent news organization focused on inequality and innovation in education.

An earlier version of this article stated incorrectly that the SAT went virtual in the spring.