A massive DDoS attack hit encrypted email provider ProtonMail, experts believe it was powered by Russian hackers.

On Wednesday morning, ProtonMail informed customers that its systems were under attack that was causing a delay in the delivery of the messages.

Anyway, the company highlighted that the emails systems did not suffer further problems, such as the data leak.

Some users faced problems while using the ProtonVPN service.

The experts sustained that the attack was prolonged and the operations were restored roughly three hours after the announcement.

“The attacks went on for several hours, although the outages were far more brief, usually several minutes at a time with the longest outage on the order of 10 minutes,” reported ProtonMail.

DDoS attacks are ordinary problems for ProtonMail, but according to the company, this attack was exceptional.

DDoS protection service Radware took more time to completely repel the DDoS that according to ProtonMail peaked at 500 Gbps. Another detail shared by Radware is that the massive DDoS leveraged multiple vectors, including several UDP refection attacks, multiple TCP bursts, and Syn floods.

“The attacks went on for several hours, although the outages were far more brief, usually several minutes at a time with the longest outage on the order of 10 minutes.”ProtonMail explained on Reddit.

“While we don’t yet have our own measurement of the attack size, we have traced the attack back to a group that claims to have ties to Russia, and the attack is said to have been 500 Gbps, which would be among the largest DDoS’s on record,” 

While some of the experts blamed Russia for the attack, Radware reported that the attack was launched by systems located in the UK.

According to Bleeping Computer, behind the attack, there is a hacker group named Apophis Squad.

“In a private conversation with Bleeping Computer today, one of the group’s members detailed yesterday’s chain of events.” read a blog post published by Bleeping Computer.

“The Apophis member says they targeted ProtonMail at random while testing a beta version of a DDoS booter service the group is developing and preparing to launch.”

The leader of the group told Bleeping Computer that their first attack downed the encrypted email provider for 60 seconds,

Initially, the Apophis Squad was not interested in harass ProtonMail, but decided to prolong the attack after ProtonMail’s CTO, Bart Butler, responded to one of their tweets calling the group “clowns.”

Today the group continued to target ProtonMail with another DDoS attack consisting of a TCP-SYN flood that peaked at 70 Gbps.

ProtonMail wasn’t the only target of the hackers, they also targeted Tutanota for a short time.

The Apophis Squad group is currently developing a DDoS booter service that they advertised in the last days on Twitter and on Discord. Their service promises multi-vectors attacks leveraging NTP, DNS, SSDP, Memcached, LDAP, HTTP, CloudFlare bypass, VSE, ARME, Torshammer, and XML-RPC.

The group is based in Russia, but in a private conversation with BleepingComputer, the group said that it isn’t so.

Pierluigi Paganini