What is the source of intelligence in creatures such as the aids virus which can enter a body, know exactly?

what kind of cell to seek out and inhabit, and how and when to leave that cell later to attack body tissues? How can living things like an aids virus have what appears to be a native inherent intelligence that even appears cunning and resourceful?

First off, viruses, like HIV, are not considered living things.

Beyond that, there is no source of intelligence, just a high rate of mutations. Gaining entry into a cell is a matter of having the right code or key and with the thousands of mutations possible, it's a matter of time before one of them is right. Things that allow viruses to become more efficient happen by chance, but these successful mutants are then able to multiply faster, allowing their DNA or RNA to become dominant.

intermolecular interactions

They aren't intelligent, they just react to certain proteins and fool the system by using a certain protein. They then are encoded to enter a cell and then they reproduce.

There is no real intelligence involved. It is basically a process of 'whatever works'. Viruses that cannot infect cells and replicate don't exist because they can't replicate.

If humans couldn't reproduce we wouldn't exist very long either.

So basically, the only reason such viruses exist is because they just happen to work. The viruses don't 'know' what to do. It just happens because that is just how they survive. The ones that just happened to invade cells and evade the hosts immune system survive, and the ones that don't...don't survive.

Basically, if the viruses mutated and changed faster than the host's immune systems could change then all humans would eventually die from viral infections (in several generations).
Therefore our immune system needs to constantly keep changing in order to keep up with the constantly changing environment.
This is known as the Red Queen effect. "You need to run as fast as you can just to stay in the same place."