PLEASE READ EVERYTHING. My macbook pro is with virus. What should I do?

Question

     Hello Guys! Thanks for reading this. First, I ask apologize for any mistakes (I'm not a native speaker neither I live in a country that English is the official language).
     I've used an anti-virus called "virus barrier express" for some time (it never detected any malware) and it doesn't detect any today. I've experienced some problems (such as speed reduction, but i found it normal). My macbook pro is from late 2012 and here the specifications: Processor  2,5 GHz Intel Core i5 Memory  4 GB 1600 MHz DDR3. I have 432,6 GB free memory of 499,25 GB. I still use Mountain Lion. I was pretty sure it had a malware then I installed the Comodo Anti-virus. I was that sure because of three things:
      1- In several unrelated sites some words appeared green and when I passed the cursor over them (most of the time unintentionally) it opened sort of a box or little window. It appeared and "X" at the "right down"(think about the the screen of the mac, it would be near the trash) corner of the box then I clicked in it and the box closed. (these is similar to the "hot words" on windows).
     2- When I load a youtube video (not sure if it has begun yesterday or the day before yesterday) the description, the commentaries and the suggestions (suggested videos) keep going down (I know this sound very weird, but I'll try to explain it: I need to scroll down the page to read the description and every 1-3 seconds I need to scroll down again because the description is a little "downer". This happens "in blocs" (it doesn't scroll down continuously as i do when scroll down, it go "jumping spaces"). P.S.: the video and the search bar don't move). I'm not sure I explained right, any doubts ask me.
     3- Several times when surfing the web new windows (tabs) open with non-related things as "how to work from home and win R$16.000 (this was an aleatory number, and R$ is the real/reais = Brazil coin) and "Gold scheme: how to win the lottery" (this was translated from Portuguese).
     4- The most urgent problem (only appeared after installation of Comodo Anti-virus)  My macbook pro is constantly stopping. Example: if I try to open the Library folder (after I explain why I was trying to open it) it stop and I need to force the computer to shut down by pressing the power button and holding it. I can't think in ant other examples right now but since yesterday I have need to force the computer to shut down sometimes. This continue even if quit/exit Comodo anti-virus.
     Continuing the history… I ordered the Comodo to scan my computer and it has found 2 malware at a Library folder and 1 malware at System folder, I've tried to put them in quarantine, but the computer stopped (I don't know if it is the right term: the colored disk appeared and the computer didn't accept any command) and the malware is still there (I tried to put them in quarantine but the computer stopped again). The danger of the threat is low accordingly to Comodo Anti-virus.
     What should I do? If I remember something more I'll add it later.

Answer 1

First, remove Comodo. You don't need it, and it sounds like it is causing a problem.
The other symptoms sound like you have adware installed. Comodo might have detected some components of that adware, or it might not have, but whatever the case, you should NEVER allow any anti-virus software to quarantine or delete files from your computer. See: How to remove infected files.
Regarding the adware, see my Adware Removal Guide.
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