Q: About *.local, 169.254/16.  If router is shared by multiple macbook users, would it be possible for them to infiltrate my macbook?

RS,

First, connecting to the network, any network, does allow other users on that same network to communicate with your computer.  But, by default they will not be able to get into your computer unless you have allowed them to, by sharing files or folders for example.  You can go to System Preferences -> Sharing to see what you have shared on your computer.

What is the remote control application that your tech installed?  Most of the remote management tools out there require an account of some kind to either access the remote management console, and/or will require a username and password to access the computer itself.  This might be something that you would ask your tech guy about.

To be absolutely sure there has not been some remote control software installed, you would have to scour the system for any software you do not recognize.  You can start by looking in the Applications folder.  Also run Activity Monitor and look for any processes that seem suspicious.  Unless you are quite familiar with OS X, you will see a lot of processes running that you do not recognize, so this might not be a rewarding activity for you.  If you trust your tech guy, I would suggest asking him to review your machine and making sure it is secure.

Lastly, to check access to your files, open Finder and go to the folder which contains the files you wish to check.  Change to the list view (the icon with the horizontal lines), and look at the "Last Opened" column.  This will tell you the last time the file was opened.  Aside from that, there's not much you can do to see if they have ever been copied or opened.  If all the previous steps have been resolved to your satisfaction, then this last step is probably not something you need to be worried about anyway.

Your best protections going forward are:

- Choose strong, complex passwords for ALL of your accounts (your computer, email, web accounts, this forum), and change them regularly.  Unless you have a remarkable memory or very few accounts, you will need some piece of software or a notepad to keep track of them all.

- Don't use the same password for all of your accounts.

- Don't download or install software from anyone you don't know.  If you're not sure, do a search on the software fist to see if anyone has had problems with it.

- Don't follow links in emails unless they are from a source you know.  Even if it seems to be from some company you are familiar with, if you see strange grammar or lots of mispelled words, it's probably a fake.

- Don't give access to your computer to anyone you don't trust.

Hope this helps.

You wrote:

First, connecting to the network, any network, does allow other users on that same network to communicate with your computer.  But, by default they will not be able to get into your computer unless you have allowed them to, by sharing files or folders for example.

IF THEY KNOW YOUR USERNAME AND PASSWORD TO LOG INTO THE MACBOOK AIR AND CHANGING WILL NOT HELP, HOW FAR INTO THE COMPUTER CAN THEY GO?  IT WOULD SEEM THEY COULD GO TO THE FILES AND FOLDERS AND CHANGE THE SHARING OPTIONS FROM WHAT I SET THEM AT. 

You can go to System Preferences -> Sharing to see what you have shared on your computer.

MacOS is inherently a Multi-User System. If you choose to create only one User, that does not change anything. Each User's files are protected from the other users on the machine, even when there is only one User.

No one gets access to your files, either locally or remotely, unless they have your user-id and password. No one gets access to your computer at all unless you have turned on Sharing features in:

system preferences > sharing

Here's the correct statement then:

Macs running OS 10.x have yet to have an actual virus by definition reported at this time. Has anyone here with more than 8 points ever said "macs don't get virus?", no, no one with half a brain says the can't, they just have not at this time, that's the difference.

Securities labs who among other methods compare applications for OS X offered on the web and their payloads have yet to find an actual mac virus at this time.

Those same securities labs also identify potential points of failure with the OS and can present the developers of that those OS's with a estimate of how those failure points could be exploited either as a working model or a white paper outlining the pitiful. They do not specific if an actual variant is created. This information is shared with Apple and Apple can address these caveats with securities patches and often do, and like the securities labs they do not disclose the methods they used to address the issue, often they dont even cite the issue.

so here are the steps to protect your mac:

1) Keep your device updated from Apple Computer. This is the primary security solution to Mac OS X. Avoid Mac AV products from "reputable windows compatible" developers, most of these products have been cited as causing more issues then they fix and reporting false or erroneous information. These products are generally slap-dash Mac compiles of actual working Windows products that should be avoided at this time.

2) Practice safe browsing habits and stay off torrent and share sites or any other location that provides potentially compensated versions of pay for software or bundle malware and adware for software that can be obtained by legitimate developers.

3) Dont let anyone come into your house, sit down at your computer and install a root kit because the OS prevents this from happening remotely. Do not let an "authorized technician" you contacted via a pop up add warning you about the "virus" found on your mac install software that is intended for legitimate technical use but could be used for less scrupulous means.

4) turn off file sharing if you enabled it, turn of screen sharing if you enabled it, turn off remote desktop if you enabled it. By default OS X keeps these are off.

Make sure your gatekeeper is set to the allow software from either apple or apple and authorized developers.

How to connect with File Sharing on your Mac - Apple Support

OS X Yosemite: Allow access using Remote Desktop

OS X Yosemite: Share the screen of another Mac

OS X: About Gatekeeper - Apple Support

5) Get your securities information from legitimate websites and not uninformed blogs or media outlets that are far more concerned with providing misinformation in return for clickbait ad revenue. Sites which report securities labs found an exploit (which the labs often do post what those exploits could be), then pretend those exploits are some code that was released on the web when they were not and it the exploit never saw past being a white paper on how this might be made; those are the ones you should avoid.