The encrypted email service revealed on Thursday the extent of the distributed denial-of-service (DDoS) attack which began on Tuesday, 3 November. The attack, which sent vast amounts of traffic to ProtonMail leading to the overload of systems to the point that legitimate traffic could not get through, has stopped -- but the service has warned it may come under attack again.
ProtonMail is used by the privacy-conscious to protect their online communication. Everyday members of the public, activists, journalists and whistleblowers are known to use ProtonMail, which caters for over 500,000 users worldwide.
The service says just before midnight on 3 November, ProtonMail received blackmail from a group of hackers called the Armada Collective, believed to be responsible for a string of recent DDoS attacks across Switzerland in recent weeks. The threat, originally ignored, was followed by a DDoS attack which took ProtonMail offline for 15 minutes.
The next attack arrived at 11am the next morning before ramping up in volume and sophistication -- leaving ProtonMail floundering in an attempt to stem the flow of illegitimate traffic.
The encryption service says the assault reached 100Gbps and not only attacked the ProtonMail datacenter but routers in Zurich, Frankfurt and other locations linked to the ISP -- eventually bringing down the datacenter and ISP.
This not only took down ProtonMail, but other companies were affected, too.
In an attempt to stop the DDoS onslaught and due to "pressure by third parties," ProtonMail "grudgingly" agreed to pay the cyberattacker's $6000 ransom to "spare the other companies impacted by the attack." Nevertheless, the attack continued even after the Bitcoin-based ransom was handed over.
"Attacks against infrastructure continued throughout the evening and in order to keep other customers online, our ISP was forced to stop announcing our IP range, effectively taking us offline," the company says.
"The attack disrupted traffic across the ISP's entire network and got so serious that the criminals who extorted us previously even found it necessary to write us to deny responsibility for the second attack."
ProtonMail suspects that two hacking groups have been involved in the service disruption and most likely the second group is state-sponsored -- and "were not afraid of causing massive collateral damage in order to get at us."
The company says it is working with others to find a way to mitigate the risk of another DDoS attack, but the "unprecedented" size and scope means "finding a working solution is not easy." The Swiss Governmental Computer Emergency Response Team (GovCERT), Cybercrime Coordination Unit Switzerland (CYCO) and Europol are all involved, but the costs are mounting.
"Because of the sophistication of this attack, we will also need to resort to quite expensive solutions which will burden our finances. It is for this reason that we are also collecting donations for a ProtonMail defense fund," ProtonMail says.
The defense fund, which has raised $12,887 out of a $50,000 target at the time of writing, is a way to improve the firm's infrastructure to protect ProtonMail against other attacks of this magnitude. At the time of writing, the service is still unavailable.
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