Apple`s announcement of a major vulnerability in the iPhone, and an urgent update to fix it, could panic anyone who uses one.

Users of iPhones, iPads and Macs have been urged to install the fix as soon as they can, to ensure they are not targeted by a hack that appears already to have been used on some people.

The danger posed by such a vulnerability is high, even if the fix is simple. And the effects of it could be disastrous, even if most people will never know it existed.

It is the latest major flare-up in an ongoing battle for control and entry into iPhones. On one side stand the hackers - often employed by governments - who are constantly searching for a way into the devices; on the other are Apple, security experts, and iPone owners themselves.

There will, however, almost certainly be more. Any device that is connected to the internet is a potential target for hackers, and there is never such a thing as perfect security for ever.

However, for most, fixing the problem is simple enough: users can download and install the update, which patches the vulnerability, and are back to being as secure as they can be.

Hackers are constantly looking for bugs of this kind so that they can be sold on. Probably the most famous example is Pegasus, a piece of spyware that is thought to have been used by a number of governments and allows access into iPhones at which point hackers are able to read the owner's messages, follow their location, and listen to and watch them through their microphone and camera.

Such powerful software has only been possible because there is a whole marketplace for finding such bugs. If a hacker finds a significant problem, such as the one addressed in the new software update, they have the option of selling it on to spyware companies those spyware companies can then weaponise it and sell it on to entities such as nation states, which are able to deploy it against dissidents or other enemies.

Update to iOS 15.6.1 as soon as you can

Apple doesn`t give any more details about the iPhone vulnerabilities fixed in iOS 15.6.1, to avoid more attackers getting hold of the details. But it goes without saying that this update is a big one, and without information about who is a target, the most sensible thing to do is update now.

"Apple iOS 15.6.1 is an important update," says independent security researcher Sean Wright. He says it's possible the two vulnerabilities "could be chained together to allow attackers to remotely gain full access to victims' devices."

Taking this into account, he recommends you update your iPhone to iOS 15.6.1 as soon as possible.