Further, these third-party sites could, in turn, be dependent on resources from other domains, leading to a dependency chain of more than 30 domains - all underpinned by a form of implicit trust with the original website.

And the bigger and more complex the dependency chain, the greater the threat of malicious activity, the researchers concluded.

Professor Dali Kaafar, Information Security and Privacy research leader at CSIRO’s Data61 and scientific director of Optus Macquarie University Cyber Security Hub, said that although these webs of dependency were common and due to web design decisions, the implications on security and privacy were often overlooked.

“Almost all websites today are heavily embedded with tracking components," Professor Kaafar said. "For every website you visit, you could be unknowingly loading content from potentially malicious parties and leaving a trail of your Internet activity.”

The researchers had also found that 1.2% of the third parties that were linked to the top 200,000 sites were suspicious. And, they said, JavaScript, which was generally used to improve the user experience, represented the greatest risk of malicious activity as it would execute without being detected.

“The potential threat should not be under-estimated, as suspicious content loaded on browsers can open the way to further exploits, including distributed denial of service attacks which disrupt traffic to websites, and ransomware campaigns which cost the world more than US$8 billion in 2018,” Professor Kaafar said.

“Worryingly, the original or ‘first party’ websites have little to no visibility of where these resources originate. This points to a lack of ‘trustability’ of content on the Web, and the need to better regulate the Web by introducing standardised security measures and the notion of explicit trust.”

Rectifying this issue would require the involvement of the World Wide Web Consortium and major tech firms, apart from additional research, he said.

In the interim, browser extensions like ad-blockers and JavaScript blockers would limit one's exposure to potential malicious activity.

The researchers will present their paper The Chain of Implicit Trust: An Analysis of the Web Third-party Resources Loading, at The Web Conference in San Francisco on 15 May (16 May AEDT).