Worried my mac may be hacked. Help!

If you enabled find my mac, you also (whether you realized it or not) re-enabled the guest account. You cannot have find my mac without the guest account being active.

The reason is that if lost, whomever has it needs to be able to take the device online so that find my mac can "phone home" so to speak - communicate with Apple's iCloud servers to pass on its location information.

The guest account allows access to the internet, and nothing but access to the internet, so your machine can go online and report where it is.

if you have the find my mac turned on in the icloud preferences it causes the guest account to show up. if you turn that feature off in the icloud prefs then the guest acct will disappear but there is no way to disable it since it's built in as part of the OS. 🙂

That just looks like some messed up system fonts? Did you try just rebooting to flush system caches?

Click on the Apple menu, click "restart"

No I don't think so - I think you may have some corrupted system font, or a messed up font cache.

Try - preferences/language & text/language and use the edit feature to deselect or turn off everything but english, then restart.

Yes, it is basically safe. But don't forget what it is - it is a simple convenience tool to, maybe, help you find a lost or stolen device. It is really not a security feature in any strict sense, as once someone has their hands on your machine, all bets are off about security.

Your best security is physical security - don't leave it when using in public places, keep it with you closely at airports, that sort of thing. Don't count on any remote tracking system as simple as find my mac - if it ever is needed and works, great, but odds are it will not be of much help if your device goes missing.