Anyone with physical access to your machine (whether it is Windows, Linux, or Mac) can eventually find a way in if they know what they’re doing.
Before you go thinking that Mac OS X has a severe vulnerability that makes it less secure than other operating systems, think again. Yes, it’s startling to think that anyone could theoretically walk up to your computer and gain access within minutes. This tutorial may ruffle some feathers, but it addresses a topic that a ton of people ask about all the time. There are numerous ways to reset a password with no OS X discs.
Or maybe you purchased a used Mac from someone else and they’ve got it locked down. Let’s say you totally forgot the password to log on to your Mac.