Luke Skywalker is the name given by Avira (an antivirus program) to the program that scans files on your hard disk. I don't assume it came with the asus (although it could be a trial version supplied by them), and then somebody (you, your friend) must have installed it. Check the creation date of the Avira folder in Program Files or Program Files (x86) to see
If you didn't set Windows to log the logins (see http://www.howtogeek.com/124313/how-to-see-who-logged-into-a-computer-and-when/ ) I don't think you can see the details. But if you know what you did when, having a look at creation or change dates of files and folders might prove that something happened on your laptop when you weren't using it yourself.
When in doubt, go back to factory conditions using Asus e-recovery or whatever it's called.
I didn't know brand new machines were still being sold with Windows 8.1. Did you install that yourself? Then the advice is: when in doubt, reinstall from scratch.
I have a brand new asus t-100 on which i'm running windows 8.1. I recently left it at a friends house and got it back a few days later, but didn't worry because my windows account has a password. When I switched it on I noticed that my profile pic (a selfie) had reverted to the original shot rather than the colour tinted one I had previously. Also when I logged on, a notification window came up saying something like 'LukeSkywalker' (luke is the friend I left my computer with).
I have a bad feeling that he or someone was able to bypass the windows password and use my computer. I'm hopeless when it comes to computers, can someone please tell me if theres a way i can check to see if i was accessed during that period?