I don't think I would install it, it is not in the Debian packages, or repos,.....
The library you are talking about, seems to be rather "out dated",
I you feel you must have this program, probably the best thing would be
to contact the "support" at the site where you are trying to get this program.
I did some searches for you,how to install install Comodo AV on a Debian systemlibssl0.9.8 for Debian , in debian reposhttp://stackoverflow.com/questions/17329036/installing-libssl0-9-8-on-debian-7
They say you can get the library here: http://snapshot.debian.org/archive/debian/20110406T213352Z/pool/main/o/openssl098/libssl0.9.8_0.9.8o-7_amd64.deb
This (the above ) is a download,....
But honestly, after every thing I read in the search results,....
I really do not feel at all comfortable trying to explain how to install it,
I do not think it is a good idea, it might be ok for Windows, but
I would not put it on a Debian system.
You should try contacting them, and if they offer good support,
maybe it can be installed and is safe enough,...I really don't know
though,... I certainly would not even down load it, much less install it,
even on my Debian 6 system,.... but it is your system,... do what you want.
It might help you understand better, if you read this ,: https://wiki.debian.org/DontBreakDebian
=========== additional note======
There might be somebody here that is familiar with this software, and
they can give more information,..... I am just saying, if it was me I wouldn't
even mess with it. However, I am not saying this "blindly" or off the wall,
it is my conclusion after reading some of the material in the search results,
using the key words I showed you.
It also would help if you show us exactly what the:
then it show me an error about "libssl0.9.8".
Show us exactly what the error says. They would need that information
at their "support" as well,....