The refactor viruses can be used by either sides.
If you use the virus to switch the control to your faction, you become the owner of the portal and all of the attached resonators, destroying any link and fields attached to the portal itself, but getting no AP from the action.
If instead you use your opposite faction's refactor, the portal becomes owned by "Jarvis" (or "ADA").
Switching the portal to the opposite faction can be useful to destroy links that are in the way of the construction of a big field.
Using both kinds of refactor on a portal can also let you create a L8 portal without the need to have eight L8 agents available .
gaming.stackexchange.com/users/23609/Kappei
Here is a variant of "campfiring".
Wherever the resonators are deployed (correctly or not), an undefended portal is no match to a high level player.
But an increasing number of players have their "home portal" or "work portal" directly accessible from their couch or their desk.
These home portals usually have a combination of heat sink and multi-hack mods in order for their "owner" to be able to farm efficiently on them.
To prevent them from doing so, one can deploy a portal, add four link amps on it (which are no use either for defence or farming) and then convert it to the enemy faction.
The link amps will be unremovable, and the owner will be stuck with their regular four hacks per 4 hours, unless they use a refractor/virus to convert-destroy-rebuild-upgrade.
gaming.stackexchange.com/users/52176/Romaun
You can also use other-team refactor viruses as a portal denial weapon.
Here's how: Take down the enemy's portal by normal means.
Stand directly on the portal's location and deploy eight level-1 resonators.
Flip the portal into your enemy's hands.
This leaves them unable to space the resonators properly without using a refactor of their own, but makes the portal so vulnerable to attack that they can't wisely invest much in upgrading it or linking it.
I've heard this called "campfiring" the portal, since the eight L1 resonators look like a fire at the base of the portal.
gaming.stackexchange.com/users/51983/Ben Ostrowsky
Edit:
As of 2013-11-07 there's a one hour penalty until another virus can be used on the very same portal again ( source ).
However the technique can be used to easily gain the same amount of MU for (big) fields up to 4 times by flipping the anchors.
The other faction's viruses can be used for quick-levelling.
One can gain very much AP in a very short time span from otherwise not-so-useful viruses of the other factions type.
Needed: Area with many dense portals (not yet fully linked)
A number of Jarvis viruses or Ada refactors Plenty of keys of the area or a group of players (to hack keys on the fly) How to do it: Area needs to be in the own hand, but not linked yet
(best) Pick a special portal to be the root portal Link
every portal in reach to this portal, then make as much fields as possible
Now flip the special root node portal Destroy it, rebuild it, re-link everything Repeat
We did this once and one L7 player made L8 with an AP gain of around 250k in less than one or two hours.
Let there be n portals to connect to the root node each round, then you can gain n*313
+
(n-1)*1250 =
(n-1)*1563 + 313 AP per *round
* E.g. if you have 15 portals, this gives you 23.8k AP per Jarvis/Ada and round.
gaming.stackexchange.com/users/57371/ce4
On the Comms channel, a team-member suggested another use.
A high-level user can help a newbie by destroying a portal, allowing the newbie to (poorly) place low-level resonators on the portal, convert the portal to the enemy's side and then destroy the easily-demolished portal.
It will earn them some easy AP, especially if they have enough keys to establish fields twice.
In fact, the newbie could do this directly, without the higher-level player.
gaming.stackexchange.com/users/827/Oddthinking
The refactor viruses can be used to frustrate the other faction, by removing and blocking farming modifiers on their portals.
Flip the enemy L8 farming portal to your faction (or take it down.)
Remove the multi-hack and heat sink mods (or deploy low level resonators if you took it down.)
Deploy a full set of less useful mods; common shields, link amps etc.
Flip the portal back to enemy faction.
The enemy faction will not be able to change the modifiers without flipping the portal or waiting for it to be taken down by decay or enemy agents.
gaming.stackexchange.com/users/52824/Roy
Since recent updates fields cannot overlap.
Existing long links block creation of smaller links and fields
if in the way.
Enemy weapon is useful for removing nasty long links mid-town.
gaming.stackexchange.com/users/55702/UFOslava
FARMING!
FARMING!
FARMING!
If anything, I think they are actually MORE useful.
They are useful for getting rid of friendly derp links (long nonsensical links that block potentially useful links), but also, they are great for FARMING.
Here is what you do: Build a farm of level 8 portals.
Make sure it is not too big; you should be able to burn out the whole farm in about an hour.
Deploy all four mod slots with hacking mods (3 Multi-Hacks and one Heat Sink are usually best).
Then flip the farm to the enemy faction and farm it!
They can't blow it up (because it is their faction), and they can't flip it back and blow it up for at least an hour, because ADA and JARVIS give portals one hour immunity to another ADA/JARVIS.
So, instead of wasting any of your Mod Slots on shields or other defensive mods, you can fill them all with hacking mods (Multi-Hacks and Heat Sinks) and get way more hacks out of your farm.
PLUS
you get 100 AP for each hack.
And when it's over, if you don't feel like leaving a farm up for others to use, you can just blow it up.
The only danger at all in this strategy is that members of your faction might unwittingly blow up your farm, so make sure that they know not to, and have it in a more isolated area if you can.
gaming.stackexchange.com/users/93119/prasinox
If an Enlightenment player picks up an ADA Refactor or if a Resistance player picks up a JARVIS virus, are they of any use?  (Apart from recycling!)  Each appears to be a weapon that can only be used by one side.
Are Jarvis Virus/Ada Refactors useless to the other side?
gaming.stackexchange.com
<ingress>
gaming.stackexchange.com/questions/119275
gaming.stackexchange.com/users/827/Oddthinking
The refactor viruses can be used by either side. You can use the other-team viruses as a portal denial weapon. They are useful for getting rid of friendly derp links. Both sides can use Refactors tactically to do things such as farming.
The community suggests that both side Refactors are usefull.