This is the most likely reason your phone will get hacked

Persistent pop-ups, apps you don't remember installing or unexpected changes to your home screen can all be signs that something isn't right with your phone.

Which? Tech Support regularly hears from members concerned that their phone has been hacked. 'When we deal with cases linked to hacked phones, the vast majority of the time the problem can be traced back to a dodgy app,' says Conor Houlihan, Technical Support Adviser at Which? Tech Support.

These apps can bombard your phone with adverts, encourage you to install more unwanted software and, in some cases, make it extremely difficult to regain control of your device. Below, we highlight the warning signs to look out for, how to get rid of a troublesome app and the simple checks that can help you avoid downloading one in the first place.

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How rogue apps can take over your phone

The problems caused by downloading dangerous apps can quickly escalate, particularly if they encourage you to install additional software.

Rogue apps masquerading as simple tools, such as QR code scanners and PDF readers, are among the examples our Tech Support team comes across. Downloading from the Google Play Store isn't an absolute guarantee of safety, as harmful apps have occasionally slipped through its checks.

We recently heard from one Tech Support member whose Samsung phone had started displaying 'constant pop-ups and adverts all over the screen'. The adverts encouraged them to call a number or install another app, while restarting the phone made no difference.

Our mock-up above shows some of the warning signs to watch for. The alarming 'Your device needs cleaning' message is designed to encourage you to act, while the 'Boost' button offers a vague fix. The app also asks for permission to send and view SMS messages, which a basic PDF reader shouldn't need.

In more serious cases, a rogue app can replace your phone's launcher, the software that controls how your home screen and app drawer look and behave. Conor says the team has even encountered apps that imitate the Android Settings screen, making it harder for the user to find and remove the culprit.

Most of the cases our Tech Support team sees involve Android phones. Android allows apps to be installed from outside Google Play, while iPhones sold in the UK place tighter restrictions on installing software from outside Apple's App Store. iPhone users can still encounter scam apps and nuisance browser notifications, though.

What to do if you've been affected

If you're being bombarded with adverts or suspicious pop-ups, don't follow any on-screen instructions. Avoid calling numbers they display or downloading apps they prompt you to install.

If you think an unwanted app is to blame, try the following:

• Check recently installed apps – look for anything you don't recognise, particularly apps installed around the time the problems started. For a full list of what's installed on Android, go to Settings > Apps.
• Use safe mode to remove troublesome apps – safe mode temporarily disables apps you've installed, which can make it easier to remove the one causing problems. On many Android phones, you can open the power menu, then touch and hold Power off until the safe mode option appears. Once your phone restarts, go to Settings > Apps, uninstall anything suspicious, then restart your phone normally.
• Check browser notifications – if the pop-ups are coming from Chrome, tap the three-dot menu, then Settings > Site settings > Notifications. Block notifications from any websites you don't recognise or trust (see also: the easy way to get rid of annoying phone notifications).
• Act if you've shared sensitive details – if you've entered payment or banking information into a suspicious app or website, contact your bank using a trusted number or its official app. Change the passwords for any accounts you think could be at risk, too.

Our expert's advice

'Rogue apps and unwanted pop-ups are a common issue that we regularly help Which? Tech Support members with. It can be alarming when adverts are appearing all over your phone or familiar menus have suddenly changed.

'Fortunately, we're very familiar with these problems and they're often easier to fix than they might first appear. In many cases, identifying and removing the offending app or revoking unwanted browser notifications is enough to get things back to normal.

'If you're struggling to work out what's causing the problem, we're more than happy to walk Tech Support members through the steps they need to take and help get their phone back under control.'

Conor Houlihan, Technical Support Adviser

Whether you're on iPhone or Android, it's worth adding an extra layer of security to your most-used apps. See our guide to phone apps you need to secure right away.

Quick tips to avoid dangerous apps

• Stick to official app stores – it's generally safer to download apps from Google Play or Apple's App Store than an unfamiliar website, although being listed there isn't a guarantee that an app is trustworthy.
• Check before you download – look at the developer's name and recent reviews. Be wary if people repeatedly complain about intrusive adverts, subscriptions or pop-ups.
• Don't download apps you don't need – your phone may already have the feature you're looking for. Android phones and iPhones can scan QR codes using the camera, for example, so there's usually no need for a separate scanner.
• Pay attention to permissions – be wary if an app asks for access that doesn't seem relevant to what it does. A QR code scanner asking to access your contacts, for example, is a red flag (see also: Which phone apps are tracking your location?).
• Keep Google Play Protect switched on – on Android, open the Google Play Store, tap your profile picture, then Play Protect > Settings. Make sure Scan apps with Play Protect is switched on.
• Keep your phone updated – install Android or iOS security updates when they're available, along with updates for your apps.
• Be wary of unexpected links – links in texts, emails and social media messages can lead to fake websites or malicious downloads. Be particularly suspicious if you're prompted to install an app or change your phone's settings.

10 things every smartphone owner should do to keep their data safe – our experts explain how you can help secure a device in minutes.

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