Can use an outdated/unsupported paid mod?

[Lianelli]

Dear members,

my question is the following:

I want to take an old, paid modification of which the creator and it's website have completely vanished. It has been at least a year or two since there were any updates. The last real updates on the original site, which I found at Archive.org come from 2005 and 2006.

Can I take this modification, have it re-coded to the current vB version and go on with developing it further? Of course this will be for my use only, I won't release this modification to the public.

Note: I do not own a license to this modification, but a friend of mine does.

Many thanks in advance!