It seems pretty unlikely outlook.com as a whole would be hacked without it being all over the news. However, individual accounts could be "hacked" if the passwords get leaked (pretty unlikely, but not impossible) or if you have a weak password that could be guessed or brute-forced (a term describing where someone will use a script to try every common dictionary word plus combinations of words).
In general the best thing to do is:
1. Change your password
2. Enable 2-factor authentication (you'll need an authenticator app like Google Authenticator - I believe Microsoft has one as well)
Don't use the same password for multiple websites, or basically ever. Use a password manager like Lastpass, 1password, bitwarden or dashlane because they will auto generate passwords for you that are more secure and then you don't have to remember all of them. Since you only need to remember 1 password you can make it more complex. Also you can often have 2-factor authentication on the password manager too. Once you get used to using a password manager, passwords and logins will become so much easier.
Oh, and if you're using the Outlook desktop app on a PC, then you also need to be careful of malware running on the PC. Use good anti-malware software (If you have windows 10 and you don't already have other anti-malware software, then Windows Defender will be good enough - just make sure it's running)