Erasing it completely is the only way to ensure that you will not encounter the periodic requests for passwords that you do not have. It's a condition of sale Apple's OS X license requires, and the store was remiss in not doing so. It's up to you but I'd be inclined to return that Mac for a cash refund and use the proceeds to purchase one from a more competent vendor.
The Mac's original OS can be reinstalled using OS X Recovery as explained in the above referenced Support document (step 5). If that was not Mavericks, it can subsequently be upgraded to Mavericks at no additional charge.
Follow that document - it explains how to archive your photos, music, and other essential files before erasing the Mac, so that you can subsequently reinstall them.
Apps obtained from the Mac App Store that are not already included in OS X cannot be transferred to an Apple ID different than the one used to purchase them. It's simply impossible.
Why shouldn't I have McAfee on my computer???
Because not only is it totally worthless, it is likely to cause problems.
If I don't use that for virus protection then aren't I leaving myself vulnerable against viruses and the such?
There are no Mac OS X viruses. As for "and the such" nothing improves upon what is already incorporated in OS X and most garbage like McAfee will only cause problems. Those that don't cause problems will accomplish nothing beneficial.
A much better question is "how should I protect my Mac":
- Never install any product that claims to "speed up", "clean up", "optimize", or "accelerate" your Mac. Without exception, they will do the opposite.
- Never install pirated or "cracked" software, software obtained from dubious websites, or other questionable sources. Illegally obtained software is almost certain to contain malware.
- Don’t supply your password in response to a popup window requesting it, unless you know what it is and the reason your credentials are required.
- Don’t open email attachments from email addresses that you do not recognize, or click links contained in an email:
- Most of these are scams that direct you to fraudulent sites that attempt to convince you to disclose personal information.
- Such "phishing" attempts are the 21st century equivalent of a social exploit that has existed since the dawn of civilization. Don’t fall for it.
- Apple will never ask you to reveal personal information in an email. If you receive an unexpected email from Apple saying your account will be closed unless you take immediate action, just ignore it. If your iTunes or App Store account becomes disabled for valid reasons, you will know when you try to buy something or log in to this support site, and are unable to.
- Don’t install browser extensions unless you understand their purpose. Go to the Safari menu > Preferences > Extensions. If you see any extensions that you do not recognize or understand, simply click the Uninstall button and they will be gone.
- Don’t install Java unless you are certain that you need it:
- Java, a non-Apple product, is a potential vector for malware. If you are required to use Java, be mindful of that possibility.
- Disable Java in Safari > Preferences > Security.
- Despite its name JavaScript is unrelated to Java. No malware can infect your Mac through JavaScript. It’s OK to leave it enabled.
- Block browser popups: Safari menu > Preferences > Security > and check "Block popup windows":
- Popup windows are useful and required for some websites, but popups have devolved to become a common means to deliver targeted advertising that you probably do not want.
- Popups themselves cannot infect your Mac, but many contain resource-hungry code that will slow down Internet browsing.
- If you ever see a popup indicating it detected registry errors, that your Mac is infected with some ick, or that you won some prize, it is 100% fraudulent. Ignore it.
- Ignore hyperventilating popular media outlets that thrive by promoting fear and discord with entertainment products arrogantly presented as "news". Learn what real threats actually exist and how to arm yourself against them:
- The most serious threat to your data security is phishing. To date, most of these attempts have been pathetic and are easily recognized, but that is likely to change in the future as criminals become more clever.
- OS X viruses do not exist, but intentionally malicious or poorly written code, created by either nefarious or inept individuals, is nothing new.
- Never install something without first knowing what it is, what it does, how it works, and how to get rid of it when you don’t want it any more.
- If you elect to use "anti-virus" software, familiarize yourself with its limitations and potential to cause adverse effects, and apply the principle immediately preceding this one.
- Most such utilities will only slow down and destabilize your Mac while they look for viruses that do not exist, conveying no benefit whatsoever - other than to make you "feel good" about security, when you should actually be exercising sound judgment, derived from accurate knowledge, based on verifiable facts.
- Do install updates from Apple as they become available. No one knows more about Macs and how to protect them than the company that builds them.
Summary: Use common sense and caution when you use your Mac, just like you would in any social context. There is no product, utility, or magic talisman that can protect you from all the evils of mankind.
