If you suspect your Gmail account has been hacked, check for unusual activity in your inbox, sent, drafts, and trash folders. Also, review your login activity and look out for unauthorized password changes. Take immediate action to secure your account by changing your password, enabling two-factor authentication, and contacting Google support.

Causes

• Weak or easy-to-guess passwords
• Phishing scams or social engineering tactics
• Malware or virus infections on the user's device
• Using public Wi-Fi or unsecured networks
• Outdated software or operating system on the user's device
• Sharing login credentials with others or using the same password for multiple accounts.

Solution 1: Change your password immediately and create a strong password

1. Firstly, go to your Gmail account settings and tap on Security.
2. Then, select the Password option and enter your current password.
3. Create a new password with at least 12 characters, including uppercase and lowercase letters, numbers, and symbols.
4. Avoid using personal information or easy-to-guess words.
5. After that, confirm your new password and save the changes.
6. Update the password on all devices and accounts that use the same login credentials.

Solution 2: Enable two-factor authentication for your Gmail account

1. To get started, go to your Google Account settings.
2. After that, you have to click on the Security tab.
3. Under Signing in to Google, select the 2-Step Verification option. 
4. Follow the prompts to add a phone number and choose a verification method.
5. Once set up, you will be prompted to enter a verification code every time you sign in to your Gmail account from an unrecognized device.

Solution 3: Check for any suspicious activity and revoke access to any unauthorized apps

1. Log in to your Gmail account and click on your profile picture in the top right corner.
2. Then, press the Manage your Google Account button.
3. After that, open the Security tab on the left side of the screen.
4. Scroll down to the Third-party apps with account access section and tap Manage third-party access.
5. Check the list of apps that have access to your account and revoke access for any suspicious or unauthorized apps by clicking the Remove Access button.
6. Review the Connected Apps & Sites section to make sure there are no apps or websites that you don't recognize.
7. If you find any unauthorized apps, hit Remove to revoke their access to your account.
8. Finally, monitor your account activity regularly to detect any suspicious behavior.

Solution 4: Scan your computer and devices for malware or viruses

1. First of all, install reputable anti-malware software.
2. Update the anti-malware software and run a full scan of your computer and other devices.
3. After that, remove any detected malware or viruses.
4. Now, change your Gmail account password and enable two-factor authentication.
5. Regularly run anti-malware scans on all your devices and keep the software updated.

Solution 5: Update your software and operating system to the latest version

1. Check for available updates by clicking on the Settings or Updates option in your operating system or software.
2. After that, download and install the updates as prompted.
3. If prompted, restart your device to complete the update installation process.
4. Repeat this process regularly to ensure that your system is up-to-date and secure from potential security vulnerabilities.