migrating data from an old postgres version

Hi,

A coworker is getting a new laptop and he wants to migrate some data from
his old one to the new one. So he installed postgres 9.5 on the new one and
is asking me how to migrate the data from the old 8.4 database. This
database includes postgis.

I asked him to make a network connection so that he can make a dump from
the 9.5 machine, but that seems to be tricky for him.
He is inserting a harddrive in his new laptop which has the data directory
on it.

So i went to look for a 8.4 installer but it has been EOL for a while now,
so i found no official source for that. But i found a 8.4.12 installer on
filehorse.com

Now, maybe this is overcautious, but being a linux man myself, i dislike
installing unknown software. So is there an md5 signature for that
installer around?
Or maybe a more official source for a 8.4 installer?

Cheers,

--
Willy-Bas Loos