WhatsApp has a major security bug that could let hackers do bad things to innocent people. Facebook, which owns the messaging app, has issued a rare warning about a major software glitch.

The bug lets attackers hide malicious code inside specially crafted MP4 video files. If the victim watches this video, hackers can secretly run software which lets them carry out a denial of service attack, which stops the target from accessing the internet, WhatsApp or another service.

The boobytrapped clip can also be used to in a ‘remote code execution’ assault. This means crooks could run a range of software on your phone, perhaps stealing secrets such as bank account details or using your device to target other people.

The bug affects Android users running versions of the software released before version 2.19.274 of the WhatsApp software and iOS users prior to 2.19.100. If you want to be safe, we’d advise you update WhatsApp as soon as possible.

One way to stop yourself being clobbered by hackers is to make sure no-one can send you dodgy video files.

So we’re glad WhatsApp has launched a new privacy feature which will stop you being pulled into group chats you don’t want to be a part of.

The feature was rolled out to a limited number of people earlier this year but has now been officially released to all users.

Starting from today, you’ll be able to choose who can add you to groups, letting you block dodgy people or prevent annoying friends from adding you.

This might sound like a frivolous feature, but in fact it’s a great privacy tool because people in groups can see each other’s phone numbers.

If you can take control of who adds you into these chats, then you have an extra tool to protect your identity and make sure strange or scammy people don’t contact you as well as protecting yourself from bullies.

When you’ve updated the app, just open up settings and scroll to ‘account’, followed by ‘privacy’ and then ‘groups’. You will be able to choose who’s allowed to add you to groups, with three options available.

Select ‘everyone’ and you’re wide open whilst choosing ‘my contacts’ means only friends will be able to add you.

The early version of the update allowed you to also choose ‘nobody’, which locked your account down entirely.

This has now been replaced by ‘My Contacts Except’, which will let you allow only certain contacts to add you to a group.

People you’ve blocked will still be able to send a group invitation in a private message – but this is very easy to ignore. In a statement, Whatsapp wrote: ‘WhatsApp groups continue to connect family, friends, coworkers, classmates, and more.

As people turn to groups for important conversations, users have asked for more control over their experience.

‘Today, we’re introducing a new privacy setting and invite system to help you decide who can add you to groups.

‘With these new features, users will have more control over the group messages they receive. ‘These new privacy settings will begin rolling out to some users starting today and will be available worldwide in the coming days to those using the latest version of WhatsApp.’