Do the recurring credits become immediately available as soon as the virus counter is added? Or do you have to wait until the beginning of the next turn?

Yes, they are immediately available, as clarified in the FAQ and updated in the core rulebook.

Angus Lee said:

Careful here - when Pheromones comes into play, its recurring credits are immediately available. Unfortunately, that will be zero in most cases. If Pheromones gains counters later in the turn, you won't get the corresponding recurring credits until those credits refresh at the start of the Runner's turn.

radiskull said:

Oh, I missed that the OP was asking about Pheromones and I had not checked this card before answering, so I just answered in a genral sense. Thanks Radiskull for pointing that out.

I would like to ask, then, if I have Grimoire (Whenever you install a virus program, place 1 virus counter on that program.) installed when I install Pheromones, will that one virus counter be placed before or after the recurring credit is available, i.e., will it have one recurring credit on installation in this case?

That's definitely trickier. I believe (going off of memory here) that Lukas has stated that the card comes into play with its credits (none), and THEN Grimoire adds a virus counter, but I also think I remember that he promised to clarify this sort of interaction in the next FAQ.

I think the arguments on either side are compelling, and they boil down to whether recurring credits should be treated as a "when you install" effect, or if they are placed before that.

radiskull said:

I don't know if there's an inherent difference between installing pheremones with a grimoire out and installing a cyberfeeder. I have yet to attend a tournament or event where cyberfeeder's recurring credit is not immediately available. Maybe it has to do with the fact that pheremones has to have at least one virus counter on it… I hope they do clarify it, cause, as it stands, this is a very weird interaction.

Lucas's ruling goes on the thought process that Grimiore's trigger is installation, therefore happens after something is installed. Recurring credits are placed initially as part of the installation process.

The real tricky thing about pheremones is the interaction between unused recurring credits and having virus counters wiped. The rule book (pg 22) states this about recurring credits "Recurring credits are placed on a card when the card becomes active, and can be used immediately. Any recurring credits a player spends are replaced on their host card at the beginning of that player’s turn. A player can only spend these credits as instructed by their host card."

Note that it does not say they are removed, just replaced. This means that any unused recurring credits that are on pheremones when virus counters are purged will stay available until used and, once spent, will only be replaced/refreshed at begining of the runner's turn *if* there are enough virus counters to support them.

Coincidently, the way that recurring credits work can also make net police work better or worse (better if you have it rezzed before you trash their links with foxfire, worse if it is already rezzed on the turn the runner plays rabbit hole and runs your tracer ice/bernice mai)