Cult of Sirius
Official Entry: " This bizarre cult has whipped up a religious frenzy following the appearance of the Dimensional Gates. The cult has long believed in redemption of the human race by a superior Alien race. They believe the UFOs and Aliens to be harmless and are rapidly gaining credibility and recruits from the general populations. This represents a considerable threat to X-COM because the cultists will do anything to assist the Aliens in their purpose, whatever that might be."
- Quickly and repeatedly raiding the Cult Temples at the beginning of the game can yield massive cash income, Agent experience, and tactical points for X-COM's weekly evaluation. And X-COM needs only to fear retribution from the Cult itself,) for such actions.However, the Cult CANNOT retaliate until its balance is positive, and repeated raids will make the cult financially in so much debt they can't do anything for months. Thus, large scale, senseless destruction in later weeks, once per week, can keep the cult entirely emasculated.
- However, raiding the cultists can leave all your agents either very dead or very injured. Just remember that you are using basic weaponry at the start of the game, and cultists are using Marsec Heavy Launchers, Megapol Plasma Guns, MiniLaunchers, and Proximity Mines (as general explosives). The upside to that is that it is possible to obtain those weapons early by raiding the cult.
In the new XCOM: Enemy Unknown game there is a similar group introduced in the Enemy Within DLC called EXALT. While at first they may seem similar, and EXALT could still be written as the precursors to the Cult of Sirius, one operational difference between the two groups is that the religious structure of the Cult speaks of humans subjecting themselves to their new alien overlords, while the extravagance of the EXALT Headquarters suggests powerful people in Black Market and clandestine circles, groups whose interest tend to lie in acquiring power for themselves.
However, in XCOM 2, the main human collaborators are known as the Advent Group: released information suggests they are not derived from EXALT survivors, and their admiration of the aliens and propaganda seem more in the style of the Cult of Sirius.