SYDNEY - Social media algorithms are a powerful feature of online life, serving up content to users based on their browsing habits or personal data.

Australia could soon give citizens the choice to opt out of them under new legislation that also threatens big tech companies with fines if they fail to protect young users from harmful content.

Here’s what algorithms do, and the arguments around their effects.

What is an algorithm?

Open TikTok, Facebook, Instagram, YouTube or other platforms and you’ll see a scrolling feed or recommendations bar showing content targeted to your interests.

These posts are selected for users based on programming rules called algorithms that predict what you will engage with – whether it’s something you like, or that riles you.

Broadly speaking, the recommendations are based on what the machine knows about you: what you’ve interacted with or posted about online, or information such as your age, job, location and marital status.

Social media giants usually keep the coding behind these algorithms – the so-called “secret sauce” that drives traffic to their platforms – closely guarded.

Are they addictive?

It’s a familiar pattern for many – open your phone on a break and before you know it an hour has passed and you’re still scrolling.

That’s by design, researchers and activists say.

“These platforms have engineered addictive features that keep children and adults online longer than they intend, often at the expense of sleep, wellbeing and real-world connection,” Mark Williams, honorary professor of cognitive neuroscience at Macqu...