Google warns users to monitor their accounts for suspicious activity (photo illustration by Chesnot/Getty)

As Google prepares to delete millions of Gmail accounts for security reasons, the company is also warning its users to look out for signs that they have been hacked.

From December 1, Google will delete accounts that have not been used for at least two years, because they are more vulnerable to attacks. This is because they are less likely to have two-step verification set up and because they have older passwords that may have been leaked in a previous hack on the dark web.

However, accounts that are used regularly are still at risk from hackers, and Google has issued three warning signs to look out for.

The first possibility is that someone other than the account user changes the account information, including the password or recovery phone number. While the former is easy to detect, many others may not check account details regularly. Changing the recovery phone number could allow a hacker to take control of your email.

In other cases, a hacker may delete your account entirely after use or find some other way to prevent you from logging in.

If you notice any of the above and suspect that someone else has logged into your account, the first thing you should do is change your password immediately. Not just for Gmail, but for all apps and websites for which you used the same password. Sign in with your Gmail account.

Use two-step verification to protect your account (Photo: Getty/iStockphoto)

You will also need to change the password in your Google password manager.

Then check if there are any suspicious activities.

How to view your Gmail account activity

  1. Go to your Google account
  2. Select Security in the left navigation pane
  3. In the Recent Security Events window, select View Security Events
  4. Check for suspicious activity:
  • If you see activity that wasn’t yours: Select No, it wasn’t me. Then follow the onscreen steps to secure your account
  • When you complete the activity: Select Yes. If you still think someone else is using your account, check if your account has been hacked
  1. Then check which devices are using your account
  2. In the security section, click ‘Your devices’ and select ‘Manage devices’.
  3. Check if there are any devices you don’t recognize.
  • If you find a device you don’t recognize: Select “Device not recognized?” Then follow the onscreen steps to secure your account
  • If you detect all devices but still think someone else is using your account: Check if your account has been hacked

Once you’ve verified both your account and your devices and are sure they’re secure, you’ll need to enable two-step verification if you haven’t already. This means that your account should be safe even if your password is stolen.