I'm not sure this is a bug.
I only know this is this way the original game works.
I believe this is intentionally done to prevent your game from running indefinitely, since a good avenger fleet would permit you prevent any alien infiltration as long as they don't send a great number of simultaneous alien infiltration missions. This is a way to figure that time runs against humans.
If this is so, then it was pretty sloppily done. The defense against Infiltration is simple: Get Hyperwawe Decoders ASAP, build 100% world coverage even if you would have one or two "normal" bases and the rest to be just access lift, Hyperwave Decoder, General Stores (to hold the ammo) and a couple of Hangars to hold Interceptors so that you can shoot down everything quickly. Then shoot down any small UFOs which are on "Infiltration" mission as soon as they appear and the aliens will never get to the point of signing any pacts.
Well, also when I had only the lowly Radars, what I did was to build 8 bases right at the beginning of the game. At the first day I ordered 7 bases having a radar to spot any UFOs and an armed Interceptor to shoot it down. Before the end of the month I could destroy them all. I then bought truckloads of Avalanche missiles and shot down everything that was "Small" or smaller. My abilities to do some speedy research were initially pretty limited but I was able to contain the alien's invasion to small UFOs only, collecting the loot until I got enough money to build additional labs and put scientists into them.
Basically, the aliens could manage to do some scouting pretty unhindered during the first 26 days but after that they had really BIG troubles getting any scout down to Earth and back. And if they tried to do Terror during the first month, I took the commitment to shoot that dreaded Terror Ship down even if I had one or two Interceptors down. And despite
the defendability of my detection bases being rather pathetic, they could not even do any retaliation because the Battleship seems to not contain any detection ability so if all the small scouts got destroyed, they could not figure out where that pesky base of mine actually is when the Battleship was ready to do the attack.
And I was still able to capture a Navigator to get a Hyperwave Decoder. I was even able to obtain the Psi technology during the wait: the Ethereals showed up and as I had my Stun Rods ready from the day 3 (the first 2 days they were in the mail
), I took my time to capture one alive.
This strategy worked because the alien's AI was quite stupid (at least at the Begginer difficulty, see below). The aliens tended to send the UFOs one after another at least early in the game. During the first month they probably did only "Research" (which makes sense, you can't do anything more complex to the human race when you don't know where it is living and how it is living so on and so forth). Later when the search&destroy system was in place, they kept sending a single small UFO every now and then and see them disappear into thin air instead of sending a swarm of them in an attempt to discover why these scouts are disappearing.
I was thinking that when I shot all these scouts down, they could not figure out any suitable location for the Infiltration and thus did not bother trying to Infiltrate. However
this place seems to suggest that it is probably not the case but I am not sure. What I know is only that when I shot down the scouts, the aliens would not send the last wave containing the main crew.
So I don't know if the bug is in the "instant success" thing of the last phrase of Infiltration or it is in the ability of the player to render the mission impossible by killing the scouts but there has to be a bug somewhere.
To be honest I was playing only "Easy" difficulty. I don't have any experience from the harder versions of the game and I don't have any experience doing this in the OpenXCom (I am goint to fix that as I have OpenXCom armed and ready). And also I liked this kind of "alien stupidity" because that allowed me to hold them back until I had my
assault combat equipment ready. Then I allowed them to do selected missions (so I could receive more resources to expand my initial combat kit
).
