Ethiopia has cut off internet access nationwide until at least June 8 to try to stop cheats from posting high school exam papers on social media, a government official said on Thursday.

Hundreds of thousands of students will take the tests throughout the Horn of Africa country with Grade 10 exams taking place from May 31 until June 2, and Grade 12 tests from June 5 until June 8.

Last year, exam papers were widely posted online, prompting the government to reschedule the tests, which are the main public exams for 16- and 18-year-olds to secure places at university and on vocational courses.

“The shutdown is aimed at preventing a repeat of leaks that occurred last year,” Mohammed Seid, public relations director of Ethiopia’s Office for Government Communications Affairs, told Reuters.

“We are being proactive. We want our students to concentrate and be free of the psychological pressure and distractions that this brings.”

Mohammed did not give a precise date regarding when the shutdown would be lifted, but added it would last throughout the exam period.

He said only access to social media outlets was cut off and that services such as airline bookings and banking requiring internet access remained intact.

A Reuters witness confirmed that WiFi and cellular internet access has been cut off. Access at embassies and international organizations remained intact.

It is not the first time that Addis Ababa has pulled the plug on the internet. At the height of protests in late 2015 and 2016, Ethiopia imposed a blanket ban for weeks before disrupting only social media outlets such as Facebook and Twitter.

At that time, rights group Amnesty International slammed the disruption as an “intent on stifling expression and free exchange of information.”

Critics say Ethiopia, an important Horn of Africa ally of the West sandwiched between volatile Somalia and Sudan, often clamps down on freedoms under the guise of national security. The government denies the accusations.