Brother-in-law used my computer. Am I right to be worried?

[AmIRightToBeWorried?]

I would be grateful for your thoughts on whether I'm being rightfully suspicious or not. Am I just being too paranoid or would you be worried if you were in my shoes? Do my suspicions sound too far fetched? How could I go about confirming my suspicions? Is spyware usually too difficult to be detected even with the help of someone with great knowledge on such matters?

As I was visiting my wife's family I was staying in my mother-in-law's home where her brother lives and my wife's brother (around 30 years old, her other brother is a programmer) said that his laptop battery was malfunctioning and it was being fixed. He had a very old MacBook that he was trying to use while his new laptop's battery was being replaced but he told me that as he tried to install a pirated Microsoft Office package into the old Macbook it crashed so that he wanted to boot the old Macbook with an OpenCore Legacy Patcher and asked for my computer in order to be able to install the Patcher into his external hard drive and I agreed. He also put some files from his external hard drive into my desktop as the external hard drive was going to be reformatted with the OpenCore Legacy Patcher.

Afterwards I started to feel suspicious that this whole thing had just been a pretext in order to install some spyware into my computer which I believe could have been done in this way since I needed to give my password two times in order for the Patcher (which maybe was a Trojan?) to be installed or maybe the files that were moved from the external hard drive to the computer were spyware?

The reason I'm being suspicious is that I feel like my wife's brother who I'm not close to at all could have asked for someone else's computer to do it including his own brother's computer, but maybe I'm just being too suspicious but I think a spyware definitely could have been installed in this way from what I've read about such things.

In addition her brother is a skilled programmer so I believe he definitely has the required skills to install spyware into my computer in such a manner should he be interested in doing so.

 

[ericwn]

You have suspicions, that’s all that matters. Reinstall the os from scratch, apply your first backup prior to that incident and never look back.

 

[Jay-Jacob]

If you are worried/suspicious then reinstall OS from scratch and use your older backups get files back. In future best don't give anyone access your Mac to install anything, but if really need to then create guest account so they can't put anything on main account and delete guest account after they done. Maybe that way help be less suspicious in future?

 

[ThrowerGB]

One gotcha with reinstalling from backups, is that you lose any the changes you've made to any of your files, directories, or apps, etc in the time period between the backup you're restoring from to the current time. This includes any new files. This is not to say you shouldn't be backing up. I backup to both local TimeMachine disks and to offsite cloud storage.
In your situation, you might first try running anti-virus software to see if it can find anything amiss. You should choose an anti-virus that's highly rated. I use the Sophos product Sophos Home. It not only looks for problems, but also includes tools for removing most problems. You can get a free trial. Try it. if you like it, keep it. It doesn't cost much. If not, it comes with an uninstaller.

 

[kschendel]

I would wonder what you might have on, or be doing with, your computer such that your brother-in-law might want to spy on it? I have an extended family member who thinks that people are always spying on his computer; I try to tell him that nothing in his life is interesting enough for anyone else to spend even 5 minutes on. I would also point out that simply being a "skilled programmer" doesn't give anyone the skills to install spyware. I myself am a skilled programmer in my field, but I wouldn't have any more clue as to how to install spyware than anyone else who could google.

 

[nollimac]

You can use EtreCheck to scan your Mac. A computer or phone are highly personal devices, don't lend to anyone, period. This is not about lack of trust in others either...it's your toolbox...a mechanic doesn't lend out his/her tools, right?