First off, I will say that I am a complete newbie and novice to Ubuntu. Currently, I am running 20.04.3 LTS.
So I have been dealing with a RAT that first infected my Windows PC and I highly suspect spread to my Android cellphone. I reinstalled Windows several times after wiping the hard drive and it kept coming back. So I switched to Ubuntu as a temporary fix.
I have been very cautious about any abnormal behavior exhibited by Ubuntu. I have noticed some strange behavior.
One is that an error message randomly popped up regarding focal security universe binary amd64. See photo posted below.
There was also an instance where the user login page looked different and I wondered if it was an overlay screen. Please see link of video here: https://streamable.com/gynn2t The backup logo appeared on the login screen and I could not click on it. Also, there is a brief secondary login screen after I already logged in to the first screen which makes me think it was an overlay login screen that I logged into.
There was also a file called agent.1761 and when I googled it, I found this link: https://community.synology.com/enu/forum/20/post/140792
This referenced a NAS which can be used to backup an OS including Windows and Ubuntu..
At one point, I also noticed that a network icon appeared on the login screen.
For reference, I reinstalled Ubuntu after I noticed all of this strange behavior. The current installation I have is where the error message popped up.
I also notice that the acessibility icon pops up on the login screen during night hours. I am on PST time. Hackers in other countries often log on during my night hours since it is daytime over in their region. When my Windows OS was hacked, the computer was removed into almost exclusively during my night hours.
My biggest question is how can I detect if Ubuntu has been hacked, has malware, a virus or a trojan? Secondly, how can I protect Ubuntu? I appreciate any help.
https://ibb.co/7yWgHKd
https://ibb.co/pJKSWmH
https://ibb.co/Y7yGz1P
'Error opening the cache (E: Unable to parse package file /var/lib/apt/lists/security.ubuntu.com_ubuntu_dists_focal-security_universe_binary-amd64_Packages(1), W:You may want to run apt-get update to correct these problems, E:The package cache file is corrupted)'. This usually means that your installed packages have unmet dependencies
![error opening the cache](https://i.stack.imgur.com/CpHt8.jpg)