Is there a way to validate that an apple update is legitimate? I have reason to suspect that somebody may have had unauthorized access to my computer. I've just reset my copy of OS X from the recovery partition. Afterwards, I was prompted twice to update my OS via the App Store. One of these I may have selected through a notification; the second I selected through the App Store. I'm now on 10.13.6.

Is there a way now to make sure both of these updates were legitimately provided by Apple? 

Relatedly, if somebody wanted to install malware of some kind into the recovery partition of my MacBook, is there any way either to scan and remove that or to replace that portion of the hard drive with a legitimate version of the partition?
On other software updates (and for not having any doubt about the legit of them) sudo through terminal. 

To install all available software updates, instead use the command sudo softwareupdate -i -a. The -a switch simply instructs the command to install all updates. Again, you’ll need to enter your admin password when prompted.

There’s no traditional progress bar, but you will see updated text entries in the Terminal window as each step is completed, letting you know both when certain updates have been downloaded and when the entire installation process is complete.

If you installed software updates that require a reboot, you’ll see a final message instructing you to restart your Mac. You can do this via the normal macOS interface, but since we’re already using UNIX commands in Terminal, you can also type sudo shutdown -r now, which instructs shutdown command to restart the Mac (“-r”) immediately (“now”).