The Canada Revenue Agency has resumed all online services after fraudsters used thousands of pilfered usernames and passwords to obtain government services.
The agency disabled the services Saturday after discovering more than 5,000 accounts had been the target of three cyberattacks.
Online access to “My Business Account” resumed Monday and all others were brought back online Wednesday evening.
The agency says it regrets the impacts on Canadians and has modified all its security systems to protect against future cyberattacks.
All individuals affected by the cybersecurity breaches will receive a letter from the CRA explaining how to confirm their identity in order to protect and restore access to their account.
The agency urges everyone using its online services to update their accounts with unique passwords they don’t use for any other purpose.
It also recommends all CRA “My Account” users enable email notifications as an additional measure of security.
They can also opt to use a new security feature that will allow them to set up a unique personal identification number to open an account.
About 5,600 CRA accounts were targeted in what the CRA has described as “credential stuffing” schemes, in which hackers used passwords and usernames from other websites to access Canadians’ CRA accounts.
The first of three attacks last week took aim at the GCKey service, which is used by about 30 federal departments and allows Canadians to access services like the My Service Canada account.
By using the previously stolen usernames and passwords, the perpetrators were able to fraudulently acquire about 9,000 of the some 12 million GCKey accounts.
Separately, CRA’s system was hit by credential stuffing attacks. The perpetrators were able to use previously hacked credentials to access the CRA portal. They were also able to exploit a vulnerability that allowed them to bypass the CRA security questions and get into thousands more accounts.
In addition, the CRA portal was directly targeted with a large amount of traffic trying to attack the services through credential stuffing.