Malware slows my computer in Flash player

Adobe Flash Player version 20.0.0.267

Mac OS X Version 10.7.5

Safari Version 6.1.6

So my Macbook has been running slow when running Safari and I had found out that Adobe Flash player was allowing malware to run. I had searched all of the Flash cookies that has been stored on Flash and found that some were harmless domains like Youtube (s.ytimg.com) and others, but I had also looked up other domains and I found    secure.insightexpressai.com which are suspected malware and I can feel my computer going slower when it appears. I tried to block access to these suspicious domains but after a few days or so, the block disappeared and it allows for the malware to run again. I went to the Apple store and they told me to use ClickToFlash. I do not want to install this software because I like Safari the way it is. I also asked about permanently removing the domains from terminal, they said I could use Nano. I am running the latest version of Flash player and I do not have my Safari to the latest version. What is your recommendation for keeping my MacBook malware free? I would like to consider using terminal but I need to make sure that nothing goes wrong. Insightexpressai.com is also in my Safari cookies and it reappears after it is deleted, which could be a reason why it runs in Flash soon after. I know that Adobe knows about this problem, so what is your best solution to resolve this?