Both Android and iOS devices have safety guards that help you know if your device is being used without your permission — hence why you should always check your email for alerts of login to unknown devices, even if your phone is right beside you. Sometimes, it’s not just a bug.

Given the amount of confidential information stored on your phone, from personal data like addresses and photos to credit card numbers, it’s wise to be concerned if your phone starts acting strange.

But just to be clear, these symptoms don’t necessarily mean your phone has been hacked. Sometimes the OS is just being silly, sometimes it’s slow because you have too many apps running, the battery is low, and so on. But they are still known symptoms of a hacked phone, and you should pay attention when they happen. Better safe than sorry.

Before we begin…

It’s worth noting there are some differences in security between Apple and Android.

Apple says iPhones don’t need antiviruses because their system is already made to be totally secure. Personally, I have an iPhone, and never had any security problems with it - I also never felt the need to install third-party security apps.

Android, however, is open-source - a major advantage for customizing and tweaking, but it also leaves the system more vulnerable to security attacks. Android users should be more careful, and having a trustworthy antivirus installed is highly recommended. When I had Android, I tried and recommend Avast, McAfee, Kaspersky, or my favorite, BitDefender.

Now, let’s get to the symptoms:

1. Your phone is slower than normal

Is your phone slower than usual?
Is your phone slower than usual? Source: 9to5Google

This is a bit vague, since it can come from a number of “natural” causes. Unwanted malware running in the background can greatly reduce your phone’s performance, so you should be wary, especially if it happens out of nowhere (that is, your phone is usually fast and responsive).

Strange performance symptoms you should watch out for:

  • Battery drain: background malware activity will drain your battery faster than usual;
  • Your phone gets really hot: same reason as above;
  • Apps take longer than usual to open;
  • Apps close or crash out of nowhere;

Then again, it might be nothing to worry about. Here are some harmless reasons that could be slowing down your phone:

  • A recent OS update;
  • Too many apps installed (remember: most apps update in the background, even if you’re not actively using them);
  • Low/old battery (older batteries tend to make for slower performance);
  • You need to clear space (like old photos and videos — apps like WhatsApp automatically download videos and photos you receive from groups by default);

2. You found new apps you didn’t download

Suspect apps that install themselves on your phone.
Suspect apps that install themselves on your phone. Source: The Verge

While your phone’s manufacturer can install or change a few apps on your phone after updates, they are usually upgrades.

But if you notice strange apps popping up or downloading automatically, this could mean malware. Sometimes this is done for spamming — bombarding you with ads which will consequently slow down your phone. But it can also be done to run in the background and steal your personal information.

The best course of action is to ALWAYS suspect unwanted apps and quickly make a Google Search before even clicking on it. Surely other people that have encountered the same app will help you uninstall it.

Ads popping up are annoying, but they could be just desperation. Many “free” apps, especially on Android, tend to do this — they will show you a pop-up for another app, but cleverly hide the ‘X’ to close it, or make it really small and hard to see, leading you to accidentally click on the ad. More often than not, this will simply take you somewhere you can close immediately with no harm done. Simply uninstall the app showing these ads and they should stop.

However, fake antivirus messages are a major red herring — especially if you didn’t download an antivirus to begin with. These apps will tell you your phone has been infected and you need a scan. Of course the scan will find a handful of viruses on your system and ask you to purchase their product to get rid of them. Never fall for this one. Take action immediately to remove this app from your phone.

Avoid installing apps outside of your phone’s app store. Apps from the store are usually safe, since they have to be approved by the manufacturer.

3. Websites look different and/or redirect somewhere else

Notice any strange differences on websites.
Notice any strange differences on websites. Source: MalwareBytes Labs

A famous hacker trick is to use frequently visited websites in order to steal your information. For example, you might see a fake webpage pretending to be your bank, or pretending to be Facebook. If you log in, they got your information. This is called “phishing.”

This tends to happen if you already have some sort of malware in your device. Be wary if your frequently accessed pages seem to refresh or redirect, or if they look slightly different.

This can also happen if you’re using unsecured Wi-Fi. Virtually anyone can stand on the street and create an unsecured Wifi network with the name of the cafeteria you’re in, and trick you into logging in. Avoid unsecured networks, especially if you intend on logging to accounts and/or making transactions.

4. Your phone sends messages by itself

This is a major red herring.
This is a major red herring. Source: iPhoneHacks

Friends will ask you about SMS or email they received, but you know you never sent. This can be anything from cheap insults (from someone who just wants to do you harm), to asking for money while posing as you.

This is not a symptom like “slow phone” anymore — if this ever happens, it’s probably serious.

If it gets this far, check your data usage history, and most importantly, your recent bank transactions — to make sure nothing has been bought using your card.

Receiving strange spam-y messages is also not a good sign, particularly if they sound urgent and ask you to call a number or click on a link.

What to do if you think your phone has been hacked

These are the basic steps you can take to save your data and keep your phone safe:

  • Run anti-malware software — ALWAYS downloaded from the legit app store. If you can, run more than one;
  • Manually check your app list and uninstall anything you don’t recognise;
  • Always use secured and trusted networks;
  • Change all passwords to your main accounts, especially if you use the same password for different account;
  • Reset your phone to factory settings — if the previous steps didn’t do it, this should flush out whatever was bothering you.

If you’re still having trouble, turn off your phone and contact a professional right away.

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