For decades, social media giants have enjoyed near-total immunity from the impact their services have on users’ lives.

A landmark legal verdict handed down on Wednesday in a Los Angeles courtroom changed all that.

After more than a week of deliberation, a jury found Meta, the owner of Facebook, Instagram and WhatsApp – as well as Google-owned YouTube – to be liable for addictive design features blamed for leading a teenage girl to depression and anxiety.

The verdict is likely to reshape how America’s legal system treats Silicon Valley’s tech giants and the content that is posted on their platforms.

The story of the plaintiff, known as Kaley GM, is hardly unique.

From the age of six, she became a heavy user of social media apps with feeds that go on forever, recommendation systems that surface the most compelling content and autoplay functions that stop users from switching off.

Kaley, now 20, said social media apps sent her spiralling into body dysmorphia and self-harm. In one day, she spent 16 hours on Instagram.

It is a pattern familiar to many concerned parents trying to limit screen time or attempting to get their kids off their phones.

But until now, there seemed little that would compel the companies to change their behaviour because of a landmark law which effectively shielded them from taking responsibility for their output.

In 1996, the US passed a law known as Section 230 that allows social media companies to run their sites without being held responsible for what users post there.

Since then, the legislation, called the law that built the internet, has acted as a get-out-of-jail-free card for tech companies. Only in extreme cases, such as when their services were used for sex trafficking, were companies held liable.

‘Accountability has arrived’
The California lawsuit turned this defence on its head.

It focused on the way that Instagram and YouTube were designed, rather than the content on them.

Meta and Google may not be responsible for what gets posted on their platforms – but they can certainly be held to account for how their apps work.

Read More: The historic verdict that will change social media forever