If Facebook thinks your account has been comprimised it will disable your account. You will then have to go through some automated security checks to re-enable your account.
This has happened to me once before when I accessed my Facebook account whilst on holiday in another country.
These details are from the Facebook FAQ:
When I try to log in to Facebook, I get this message: "Your account has been temporarily suspended"
You are seeing this message because Facebook has detected suspicious activity on your account and has temporarily suspended it as a security precaution. This may be because your Facebook account was accessed from an unfamiliar computer. It is also possible that your password was "phished," or stolen by a website designed to look like Facebook.
You will be able to regain access to your account once you complete the automated security verification process.
When you regain access to your account, please be sure to follow all of the suggested security precautions, including:
Password Protection: You should select a unique and complex password for your account and keep this entirely to yourself. Be sure that you use a complex string of numbers, letters, and punctuation marks that is at least six characters in length. It should also be different from other passwords you use elsewhere on the internet.
Private Browsing: Please make sure that you log out of your Facebook account and quit your browser when you’re done using the site. This is especially important when using a public computer or someone else's mobile device. You should also never check the "Keep me logged in" box when logging in from a public computer, as this will keep you logged in even after you close your browser window.
Secure Email: Since anyone who can read your email can probably also access your Facebook account, you should make sure that any email addresses associated with your account are secure. To ensure security, you should change the password for all of your email accounts and make sure that no two are the same. By varying your passwords, you can greatly decrease your account’s risk of being compromised in the future.
Security Question: If you have not done so already, you should add a security question to your account from the Account Settings page. You should choose a question and answer that you will remember, and no one else should be able to answer the question that you choose.
Log in at Facebook.com: Make sure that when you access the site, you always log in from a legitimate Facebook page with the facebook.com domain. Do not click any unfamiliar links and do not run any executable files (files ending in .exe) on your computer without knowing what they are. If something looks or feels suspicious, go directly to www.facebook.com to log in.
Run Anti-Virus Software: If your computer has been infected with a virus or with malware, you will need to run anti-virus software to remove these harmful programs and keep your information secure.
Learn More: Visit our Security Page to learn more about keeping your account safe and about how to report suspicious material in the future.