The cyberattack that occurred on June 23rd affected the email accounts of dozens of MPs and several other senior ministers, including Prime Minister Theresa May. Every MP uses the network that was compromised for interactions with constituents, the Guardian reported. MPs were told of the cyber attack on Friday night and said they were unable to access their emails the following morning.

Despite repeated warnings to choose strong passwords, UK intelligence determined that the hackers had attempted to gain access to accounts protected by weak passwords.

An anonymous “security source” cited by the Guardian said the hackers used specifically designed programs that test hundreds of thousands of different passwords combinations. “It was a brute-force attack. It appears to have been state-sponsored. The nature of cyber-attacks means it is notoriously difficult to attribute an incident to a specific actor.”

The attack “absolutely” could leave some people open to blackmail, according to Conservative MP Andrew Bridgen, who added that, “Constituents want to know the information they send to us is completely secure.”

Suspicion initially fell on foreign governments such as Russia and North Korea, both of whom were previously accused of orchestrating hacking attempts in the UK.

International trade secretary Liam Fox said the incident reinforced the notion that MPs need to take extra precaution when securing their data. “We know that our public services are attacked, so it is not at all surprising that there should be an attempt to hack into parliamentary emails, and it’s a warning to everybody, whether they are in parliament or elsewhere, that they need to do everything possible to maintain their own cybersecurity,” he said.

“We are continuing to investigate this incident and take further measures to secure the computer network, liaising with the National Cyber Security Centre (NCSC),” a parliamentary spokesperson said, and added, “We have systems in place to protect member and staff accounts and are taking the necessary steps to protect our systems.”

Oz Alashe, a former special forces Lieutenant Colonel and chief executive officer of cyber security platform CybSafe, said compromising email accounts can merely be the “first step” in a wider attack. “Email accounts represent a rich source of information for hackers, so compromising these accounts would often be the first step in a sophisticated cyber attack,” he added.