Ok....don't beat me up on this one!
As far as I know, Avast 7.7 is freeware.
You can register on the
www.avast.com site under Registration to obtain a "key" which can be inserted when asked by the program.
I am not sure how "current" the program is. Better to ask Avast Support team via email.
As for being usable and useful....it should be both.
Again, I do not know if any update is available for the 7.7 dos version.
Hopefully, one of the Avast Gurus will jump in on this thread, otherwise, contact Support at support@asw.cz