The first thing you should do if you believe your Facebook account has been compromised is to change your password. If you use Facebook as a login for apps like Spotify or Instagram then you should change your logins. This will stop the hacker from gaining access to these third-party services through your hacked Facebook account.
A compromised Facebook account can provide hackers with an abundance of personal information. Hackers can make use of this information for nefarious reasons like contacting people or sending fake credit card offers. Hackers can also use hacked accounts to send spammy messages or to post on your timeline (as the case were you who did it).
One of the most frequent ways hackers get into an account is to exploit a flaw in Facebook’s app code. For instance, a glitch in the iOS Facebook app let hackers hijack cookies and take an iPhone user’s “access token.” These tokens are digital keys that allow them full control of the user’s Facebook account and, thanks to Single Sign-On, other websites the person connects to using their Facebook credentials.
A hacker can also gain access to a user’s account through brute force attacks. This method involves figuring out passwords, mostly the most common ones like 123456789 and 1234567890. Lastly, hackers can also gain access to accounts by sifting through compromised credentials. There are several free tools that can be used to scan for stolen data, including a popular website called HasbeenPwned.