Alien Infiltration (Apocalypse)

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Alien Infiltration occurs when the Aliens directly deploy alien lifeforms into a building with a "grey-smokey-tube" effect from a UFO hovering directly above the home-cell. Observable in the isometric view (as shown left and right images).

Alien Infiltration is the ultimate goal. To sustain the Micronoid lifeforms with more suitable hosts... humans!

Alien Infiltration

Aliens Infiltrated (dropped) into a building (an infestation) may spread to adjacent buildings using the people tube network ⊗, influencing and infiltrating other organizations to continue life of the Micronoid at the detriment of their unwilling hosts. Aliens dropping into buildings is the only way to get close to humans and it is the most urgent of tasks X-Com must prevent.

⊗ People Tubes are not necessary. After a short time, aliens lifeforms will spread about Mega-Primus automatically, irrelevant of valid, or not, tube connections.

Infiltration Graph

Alien lifeforms present in any building will always attempt to influence the owners into supporting the Alien's agenda. If initial influence-progress is made, other members within the company yet not 'convinced' by the alien's rhetoric (overtaken by Micronoids) will clandestinely inform X-Com of alien interference. This information is made into a graph, updated multiple times per day. The graph button: "Alien Infiltration Graph"



The graph section is split into two parts: below the 50% mid-point, and above. Infiltration progress (top-right button) is displayed by coloured lines which show the ten most problematic organisations. The horizontal at the lower part of the graph section: Time, updates from right (recent) to left.

Graph: Initial Infestation

The initially infested building and others nearby (when the graph is checked often):

  • Initial infiltration will show a coloured flat line with a curve upwards at the beginning (the right-side edge).

X-Com must determine which building is most likely to be infested and then go land a squad of agents to clean up that infestation. If all aliens are successful neutralized, after a few hours:

  • Infiltration progress for that recently cleaned organisation will either disappear or curve downwards (then disappear later), or:

If the alien clean-up was partially successful with some aliens escaping, after a few hours:

  • Alien presence is detected in a building which is near the originally infested building and the graph will show a different organisation with the familiar flat line and curve at the end.

X-Com must now go 'bug-hunt' another building... until no more infestations appear on the graph.

Graph: Infestation Ignored

Any infested building displayed on the graph, and ignored by X-Com may either, after a few hours:

  • The coloured line may abruptly turn downwards which indicates aliens are dying off and the infiltration attempt is failing.

X-Com can ignore this downwards trend which may eventually return to the baseline of 0% indicative of no more aliens present, or:

  • A coloured line may show an almost vertical trend after the initial curve upwards but not yet past the mid point of 50%, which denotes an organisation is beginning to accept the aliens and their persuasive methods.

X-Com is urgently needed to remove the aliens from all the organisation's buildings, but if ignored, after a few hours:

  • The coloured line may continue vertically beyond the 50% threshold indicating that the majority support the alien's agenda.

If X-Com continues to ignore this infiltration progress, the organisation will finally be completely infected with Micronoids (Alien Infiltration = 100%) and will:

declare that Aliens are their friends and have become mutual allies.
immediately turn 100% hostile to X-Com ...permanently.


  • If an organisation is 100% infiltrated, any and all products on the market are denied for purchase by X-Com.
  • Aggressive actions such as Illegal Flyer and X-Com-Base Attack will become more frequent than what was previously classed as an 'extreme' action.
  • A technology boost regarding weapons and devices used in any tactical battle. (+3 to tech level)

Infestation Actions

Any UFO with a mission goal of Infiltration will proceed directly to its destination building within Mega-Primus:

1. The UFO craft starts to hover, then wobble slightly, over the target building's home-cell location.
2. A 'grey-smokey-tube' is formed underneath the craft and extends downwards towards the building's roof.
3. A bulbus section moves slowly down the grey tube and 'touches' the roof.
4. The 'grey-smokey-tube' is retracted back into the UFO.
5. A slight delay...
6. The UFO moves away, heading directly towards the nearest Dimension Gate at a slight faster speed than when it first appeared within the city.

The most common UFOs which are used to drop aliens into a building:

  • Scout Ships used in the beginning for small squads.
  • Transporters used for larger squads.
  • Assault Ships used for large squads and to survive longer in battles with X-Com and others.

Infestation interuption

A drop can be interrupted if the UFO is destroyed or disabled anytime during the 'grey-smokey-tube' effect. If a UFO is sustaining damage past its internal threshold of massive damage, abort mission, return to alien dimension, the 'grey-smokey-tube' effect may complete but no aliens will be inserted to the building.
To make sure there are no aliens in the building, an X-Com search of the building for infestation should be of the highest priority.

Alien Friends

If an organisation becomes friendly with the aliens, typically discovered by the usual diplomatic message : "...continue to oppose our Alien Friends we will remain hostile", it does not mean they are being converted. The friendship is one-sided due to the aliens recent negative affect on the organisation's enemy. The aliens do not care for their new friends. This is a result of dynamic relationships (the enemy of my enemy is my friend) and not due to alien lifeforms present inside their buildings.


A common misconception was that Aliens could perform a "100% subversion" of an organisation by dropping 'blue rain particles' over a building and was typically called: "Micronoid Rain". It was believed that such action of the UFO above the target organisation's building would immediately infect the inhabitants with Micronoids (hence "Micronoid Rain") and result in immediate 100% infiltration. This micronoid rain definition (in any variation) was proven to be incorrect. The purpose of the UFO and its 'blue-rain-effect' is to scan the building for an X-Com base (for future elimination). The blue-rain-effect does not do anything except Alien Search.

Infiltration Reference

The effectiveness (as listed in the tables below) of converting humans and how quickly infiltration will progress (time before 100% is reached) depends on:

Organization Infiltration Potential

Building Infiltration Potential
People Tube, Road None
Appliances Factory, Arms Factory, Astrodome, Car Factory, Construction Factory, Flyer Factory, Hydro-Farm, Large Flyer Factory, Power Station, Recyclotorium, Rescue Station, Robot Factory, Sewage Works, Slums, Water Purifier, Warehouse Low
Apartments, Hospital, Luxury Apartments, Offices, Police Station, Procreation Park, School, Sensodrome, Shopping Mall, Space Port, Temple of Sirius Average
Corporate HQ High
Senate Very High

Organization Infiltration Speed

Organization Infiltration Speed
S.E.L.F., X-COM 0%*
Government, Mutant Alliance 50%
Cyberweb, Energen, Evonet, General Metro, Grav Ball League, Lifetree, Marsec, Megapol, Nanotech, Nutrivend, Sanctuary Clinic, Sensovision, Solmine, Superdynamics, Synthemesh, Transtellar 100%
Diablo, Extropians, Osiron, Psyke, Technocrats 150%
Cult of Sirius 200%

*These organizations are completely immune to infiltration.

Alien Lifeform Influence

Alien Infiltration Multiplier Influence
Chrysalis, Multiworm Egg 0 none
Brainsucker, Hyperworm, Megaspawn*, Multiworm, Popper, Queenspawn* 1 weak
Anthropod, Micronoid Aggregate*, Skeletoid, Spitter 2 strong
Psimorph* 3 not used

*These aliens are not normally deployed for infiltration missions.

Advanced Tactics

If an important organisation has an appearance in the Alien Infiltration Graph, it is possible to make the aliens 'move along' and go infest somewhere else instead. If it is determined that aliens are inside a building, start the Alien Search mission (with a single agent) then immediately escape via blue-exit-tiles. The action of escape and aborting the battle will immediately move all aliens to a different building nearby irrelevant of people tube connections. The original building will be completely free of aliens which allows more time for X-Com to better co-ordinate an infestation removal later. This tactic can be used to move along an infestation indefinately but to random buildings. It is possible for the aliens to (randomly) choose the original building again.

It is also possible to prevent the UFO from hovering over a home-cell.

See Also