By Will Guyatt, technology correspondent

If you’ve visited a website today, there’s a good chance that PHP, the coding language at the centre of this news, was working behind the scenes.

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It’s a programming language used in around 70% of all websites online today. And serious security flaws have experts urging website owners to act now, with one tech body rating this hack as 9.2 out of 10 in terms of severity - about as big as it gets until now.

PHP runs on web servers - the computers that host our websites. When you load a website, PHP builds it on the spot: it could be a new blog post, your shopping basket, or the local council bin days.

It’s the most popular engine running the internet, and it’s not just for big businesses. If you’re running a side-hustle, set up an online album for your wedding, or launched a James O’Brien fan page in 2014,........

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