password backdoors

[root () sentinet demon co uk (System Admin)]

Dear all,

On the subject of back doors. I have an old Apollo box
running Domain 10.4.1
and lost the password for root, the only account. I could
not get back in and in the end had to re-install as I could
not break in. A short time later I told this story to the
HP service engineer who said that I should have given him a ring
as they have a way to get in ! He would not tell me anything
about how this would be done.

Can anyone enlighten me further into how this would be
done and if such back doors exist in other operating
systems.

Thanks.

Lyndon