For almost a week, Sudan has been almost completely cut off from the internet. It started slowly, with a series of intermittent disruptions during months of protests against former President Omar al-Bashir's 30-year rule.
Al-Bashir was toppled in April, but the protests did not end and demonstrators began demanding that the Transitional Military Council (TMC) cede power to a civlian-led government.
On June 3, as security forces violently dispersed a protest camp in the capital, Khartoum, all mobile access to the internet was cut.
A week later, after reports of killings, rapes and other abuses began to emerge, landline access was also shut down, severing the flow of information from Sudan to the outside world.
The situation is alarming, but not unique.
As more and more people rely on the internet for everything from communication to banking, authorities around the world are increasingly switching it off.
Here, Al Jazeera explains how and why blackouts happen and the crippling effects they can have.
What is an internet blackout?
A blackout happens when a country's access to the internet is completely cut, preventing people from getting online.
Cyberattacks or damage to the undersea cables that carry telecommunications signals can cause this to happen, but the most common reason is that authorities choose to turn off access.
Deliberate internet blackouts by authorities have been recorded as far back as 2005, but the practice became more widely-known after Egypt's week-long government-imposed blackout during its 2011 uprising.
Why do authorities shut down the internet?
In countries where traditional media is tightly controlled, the free flow of information online can be seen as a threat to authorities.
Limiting or completely blocking access is one tool they can use to control both citizens and the narrative around an event.
Authorities use national security and public interest concerns to justify the blackouts, which often occur in times of panic or potential instability.
recent elections in attempts to limit the influence of social media on the polls.
However, according to Alp Toker, executive director of Netblocks, an NGO monitoring internet censorship, these justifications can sometimes mask more sinister aims.
"We've seen that shutdowns are used to cover up incidents that are embarrassing. [They] are used to cover up violations of human rights, including alleged reports of killings," he said.
Critics of internet censorship also note the frequent overlap between blackouts and anti-government protests as evidence that blocks are being used to silence dissent and make it difficult for citizens to organise large protests.
In some cases, these have been justified as a necessary measure to prevent students from cheating, while in others, authorities simply did not acknowledge the blackout.
How is it done?
To disrupt the internet, authorities must order internet service providers (ISPs) to limit access for their subscribers.
Toker told Al Jazeera that while some ISPs - which are often state-owned - readily comply with these orders, others have reportedly been held at gunpoint and forced to switch off the internet.
These orders are often made in secret and carried out by ISPs on an individual basis, meaning companies can sometimes choose which kind of filter to apply.
Aside from a total blackout, content blocks and "bandwidth throttling" can be used to to limit internet access.
In a content block, access to certain websites or apps is cut. This is frequently used to shut down social media, but has also been applied to news sites and other sources of information like Wikipedia.
China recently tightened its online restrictions ahead of the 30th anniversary of the Tiananmen Square protests in early June by blocking access to the sites of international news organisations including CNN and Reuters.
Bandwidth throttling is a more subtle approach, in which signals are made so weak and connections so low that the internet is effectively unusable.
"People will generally blame their own connection," Toker said. "It's quite difficult to take that leap and realise it's also the rest of their street, it's also their city, it's their country. This means that throttling and partial restrictions on services can be used to cover up mass censorship".
Content blocks and bandwidth throttling often come before a total internet blackout.
Can people get around it?
The most popular way to bypass restrictions is with a virtual private network (VPN, which masks a user's location, making it seem as though they are in another country and so evading blocks on specific sites.
Authorities can block VPNs but backlash from foreign diplomats and companies that use them means this rarely happens.
In a total blackout, however, accessing the internet is almost impossible.
What are the consequences of blackouts?
The fallout from an internet blackout can be catastrophic and far-reaching as people's daily lives become ever more entwined with the online world.
Political - The most obvious impacts are political. Stemming the flow of information in and out of a country can throw reports of atrocities into doubt, making it difficult to mobilise the international community.
In Sudan, the blackout has hampered efforts by rights groups and journalists to verify the death toll following the June 3 crackdown or subsequent reports of human rights abuses.
Without access to social media, protesters cannot easily organise mass rallies or voice their dissent. However sometimes, blackouts can have the opposite effect and actually draw attention to the very issues they were put in place to smother.
In the case of Sudan, the country's large diaspora took to social media to slam the blackout and support protesters. Their messages have been picked up by celebrities, including model Halima Aden, and international rights groups, putting the crisis in Sudan in the spotlight.
View this post on Instagram
Ina lilah waina ilayhi rajioon.. I just wanted to take a moment to bring some awareness to to what’s happening in Sudan right now. The details are gruesome & absolutely heart breaking. There’s still so much unfolding BUT what’s happening is a violation of human rights!! The people in Sudan deserve our attention & our help. Please click the link in my bio to learn more & ALSO please consider changing your profile picture to blue in support of #SUDAN
A post shared by Halima (@halima) onJun 11, 2019 at 2:07pm PDT
Economic - Internet blackouts can do severe damage to a country's economy by limiting people's access to banking and preventing businesses from contacting each other.
Dawit Bekele, Africa bureau director at the Internet Society, an NGO focused on internet policy, blackouts also deter much-needed investment.
"Investors need the internet to come to a country, when they see that a government is shutting down the internet, they think twice before going there," he told Al Jazeera.
Netblocks estimated that the four-day shutdown in Ethiopia last week cost the country $17m, while a 2016 report by the Brookings Institution, a think-tank, said the global economy lost $2.4bn through internet shutdowns between 2015 and 2016.
Social - Disruption to the internet can wreak havoc on people's daily lives and even be a matter of life and death.
"We've tracked cases where women have miscarried because the couldn't get to hospital on time during shutdowns," Toker said.
"We've spoken with people who have lost friends and family and they still aren't able to get in touch because of the pandemonium these acts of censorship have caused."
Human Rights Watch reported this week that under the blackout, Sudanese people were unable to get updates about roadblocks or makeshift medical centres, putting lives at risk.
Bekele told Al Jazeera that, during an internet blackout in his own country, Ethiopia, he was unable to bring important medicine into the country for a friend because he could not make contact with him to find out the prescription.
"I'm sure there are thousands of these types of situations because today we depend on the internet for our daily lives," Bekele said.
Is there an end in sight?
Despite the damage they cause and a patchy success rate, internet blackouts show no signs of losing popularity.
The United Nations declared internet access a human right in 2016, but while the UN can send monitors to countries and raise awareness of internet restrictions, the body has little power to prevent authorities from imposing blackouts.
Last year, there were 188 shutdowns, according to Access Now, a monitoring group, up from 108 in 2017 and 75 in 2016.
"It does seem there's a contagion," Toker said. "Countries learn from each other and once they see that one neighbour gets away with it, countries try to do the same thing."