Canada's tax-collection agency said that the private information of about 900 people had been compromised as hackers exploited the "Heartbleed" bug, and security experts warned that more attacks will likely follow.

The breach allowed hackers to extract social insurance numbers, which are used for employment and gaining access to government benefits, and possibly some other data, the Canada Revenue Agency said.

The agency appears to be the first to report that it is the victim of an attack exploiting a flaw in software known as OpenSSL, which is used on about two-thirds of websites to secure data as it travels across the Internet.

Later on Monday, British parenting website Mumsnet, which claims more than 60 million monthly page views, said it had required all users to reset their passwords after a Heartbleed-related breach. It didn't say whether any information had been taken.

Internet companies, technology providers, businesses and government agencies have been scrambling to figure out whether their systems are vulnerable to attack since the flaw was disclosed a week ago. When researchers disclosed that they discovered the bug, they said they did not know whether anybody had exploited it to launch attacks, though it had been present in OpenSSL software for several years.

Andy Ellis, chief technology officer with Akamai Technologies, said he was not surprised to hear about the attack on the Canadian agency because there are already several "tool kits" publicly available over the Internet that hackers can use to launch attacks on vulnerable websites.

"You should expect to start seeing the attacks this week," said Ellis.

Akamai learned over the weekend that customers may have had digital keys for encrypting data exposed to attack. "I've had a crypto team working on it all through the night," Ellis said.

News of the attack in Canada came after authorities in Washington warned banks and other businesses on Friday to be on alert for hackers seeking to steal data exposed by the bug.

Lior Div, chief executive of the cybersecurity firm Cybereason, said that "even non-sophisticated hackers" will attempt to launch attacks that exploit the vulnerability with the tools that are publicly available.

"We are in a race," Div said. "People who hadn't thought about using this type of attack will use it now."

To be sure, some experts said that hackers already have plenty of easy-to-use tools for attacking networks at their disposal, so that it is hard to say for sure that "Heartbleed" will lead to a significant increase in attacks. - Reuters