This week's decision by Egypt's government to declare the Muslim Brotherhood a terrorist organization marked a stunning reversal for the 85-year-old organization.

The decades-old Islamist organization has been an institution in Egypt – albeit an underground order for many years.

The Muslim Brotherhood today is a largely a political movement (but not a political party.) It is also a social movement, providing charitable outreach, health care and other services to many Egyptians. The social arm of the Brotherhood grew stronger in years when political activities were banned.

A mere 18 months ago the world was surprised to see the Brotherhood become legalized under the auspices of then-President Mohammed Morsi, who was Egypt’s first democratically elected leader in the fallout from the Arab Spring movement in 2011-12.

Now, once again, the Brotherhood is illegal. As of this week, anyone who participates in Brotherhood activities or promotes the group either verbally or in writing, or who finances its activities, could face arrest and punishment – up to five years in prison.

Publication of the Brotherhood's daily newspaper, Freedom and Justice, was suspended Thursday.

What prompted the decision to declare the Muslim Brotherhood a terrorist group?

The military-backed government said its decision to declare Brotherhood members terrorists came in response to a series of accelerating Islamist-backed attacks, culminating in the deadliest -- this week's deadly bombing in the Nile Delta city of Mansoura. Sixteen people died in that suicide attack.

Brotherhood leadership have denied responsibility for the bombing, and the government has offered no evidence of the Brotherhood's involvement. But public anger against the Brotherhood has been growing for some time.

Morsi rose to power in 2012 following the ouster of long-time leader Hosni Mubarak. After that development – Morsi’s election came with a slim margin -- many secular Egyptians were alarmed. When their new president began enacting regulations to allow the Brotherhood to assume more powers and enshrine Islamic law into the country's legislation, they were incensed.

Even after widespread protests led Egypt's army to wrest power from Morsi in July, anger against the group has continued to grow.

Do Egyptians support the government's decision?

Richard Spencer, a Middle East correspondent with The Telegraph U.K. says there is now a general feeling of anger in the country directed at both sides of the conflict between government forces and Islamists.

"There is anger at the Muslim Brotherhood and the Islamists, and there's a lot of anger now at the army and what opponents of the army – both Islamists and non-Islamists -- see as an incredibly heavy-handed crackdown on the Brotherhood,” Spencer told CTV News Channel from Cairo.

The crackdown, many suspect, will only make things worse.

Since Morsi was stripped of power in July, the army has stepped up its attacks on Islamist militants in Sinai, trying to get the insurgency there under control.

But this week's bombings suggest that the long-simmering insurgency in the Sinai appears to be spreading into the heavily populated Nile Delta, further angering mainland Egyptians.

What will happen now to the Muslim Brotherhood?

After being declared a terrorist organization, it's unlikely there will be much chance of reconciliation between the Brotherhood and the current government.

But the group isn't likely to fold up operations either. Spencer notes that the Brotherhood is not a small organization -- it has hundreds of thousands of members.

Government forces already have arrested thousands of Brotherhood members, including its top leadership. It's also violently halted protests, leaving hundreds dead in the crackdowns.

The group will almost certainly be forced to go underground – or rather, even further underground, Spencer suspects.

That's nothing new for the 85-year-old movement. The Brotherhood was declared illegal in the 1950s and spent several decades focusing on charitable efforts before it was able to rise to power following the ouster of Mubarak.

The government says that under its anti-terrorism laws, leading a Brotherhood protest will now be punishable by life in prison. Even promoting or remaining a member of the group will be punishable, the government has warned.

But Spencer says it's highly unlikely that all of the Brotherhood's members will turn their back on the organization now and start supporting the army. In fact, it's more likely to harden the resolve of some.

"Some of them may well decide to become more radical. That's the great fear," he says.