You got an Anti-Virus and it detected and blocked a virus, what did you expect?
Now. the question is, if you weren't using an anti-virus what would have happened?
And the answer is, nothing, because that virus (VBS) is a Virtual Basic Script, it only runs on Windows. And yes, avast obviously detects viruses that would only affect Windows also.
With that said, is Mac vulnerable to viruses? Yes, in theory all systems are vulnerable. If you got a Mac to avoid viruses it would have been safer to get an abacus.
Finally, what's 'unnormal' about this?
"The program uses the following components:
• bsdiff & bspatch, © 2003-2005 Colin Percival
• Google Protocol Buffers, © 2012 Google Inc.
• libcurl, © 1996-2011 Daniel Stenberg"
It says that avast! uses libraries that are copyrighted to those developers, and credits them, what's unnormal about that?
Are you implying that you are afraid you are infected and that the virus entered that information there? The question is, why would it do that? It would be pointless, and would be revealing itself. Still, I don't see why you even think that's unnormal, it makes you sound paranoid.