I know in the current time, anti-virus isn’t exactly needed for Linux,however I still wish to install some form of protective layer. I had previously downloaded a .deb for the installation of Avast! for Linux, but the Ubuntu Software Centre gave me a warning saying the file was of bad origins. I’m at a dead end here. Any help is greatly appreciated.
This doesn't seem to be supported any longer by Avast. As the package itself is broken, your only options are to force the install, use a different scanner such as
clamav, not use a virus scanner at all, or contact Avast support to complain about the issue.