Re: Why is Comodo anti-virus linux version not in Ubuntu software center?
Nobody has time to find every single program on the internet and make them all available in the Ubuntu repositories. Some closed-source programs have licenses that prevent redistribution, too.
If you want to install these programs using Software Center, you can look for a repository or a PPA for them. When you add the PPA/repository to your system, Ubuntu Software Center will be able to recognise and install those programs, and Update Manager will be able to update them.
If no repository or PPA exists, you could ask the software developer to make a repository.
As you're new here, I'll also remind you that there are currently no viruses for Linux. The only reason you might want Comodo anti-virus is to scan for Windows viruses.
I try to treat the cause, not the symptom. I avoid the terminal in instructions, unless it's easier or necessary. My instructions will work within the Ubuntu system, instead of breaking or subverting it. Those are the three guarantees to the helpee.