The value of Facebook’s shares has fallen because of that big data breach

Facebook's under a lot of pressure after it was revealed that a firm with links to Trump's 2016 election campaign had harvested information from more than 50 million Facebook profiles.

What it means: The accusation is that the company, Cambridge Analytica, used the data to influence US voters in the election. It's been a huge scandal in both the US and Europe, and politicians have called for a closer examination of what tech firms are doing and how they work.

Investors are scared that the revelations will mean greater government involvement – or regulation What's this?  – of tech firms, which could hit their profits.

When investors buy a share in a company, they're essentially betting its profits will improve and the company will get bigger. That means the regulation What's this? shares they've bought will get more valuable. When investors get wind that might not happen, they sell their shares. When investors start selling their shares, they become *even* less valuable. The value of shares in Facebook fell by nearly $40 billion in one day.