So when downloading offline installer do you install the game files and then backup or backup the offline installer itself? Another question, are the offline installers connect to a server that sends data for you to download offline? Last question, if GOG was to theoretically go down, would the offline installers work or not work since they might be connected to GOG services? In general, how do the offline installers work, are there signal data packets given when using it? If it is is not connected to server, how would an individual create an offline installer without linking it to anything. Just curious. Thank you in advance very much for your help, time, information, and lesson that anyone will give me! Have a great day and week!

i would add just a little further info to what is already an excellent response by ryan333. some games will give you a large exe to install. antiviruses will always scan these. if you choose to back these up to a hdd/ssd, you will be fine. however, if you back these up to something like optical media, you will run into issues. the antivirus will constantly scan the file endlessly as soon as the disc is inserted. there are 2 solutions. deactivate the antivirus while you install/copy off optical media. or package the exe into an iso or similar. or just rename the exe such as game.exe.removethispart. so when you insert the disc, the antivirus won't intercept. it will give you time to copy to hdd/ssd. you won't be able to install from the optical media with the second solution because they're read only.

Whaaat??? Which games do that, and why would they do that (considering the games are not supposed to e.g. "phone home")?

Most if not all AV products offer an option to set a file-size limit. Another option commonly found allows you to exclude drives and directories to monitor and scan. I don't know about MS's AV/Malware scanners and their behavior in such case. One could also always resort to Linux without comprising security to carry out backup tasks. ;-)

There are many games requesting outgoing access - in some cases this is handled by MS's firewall without giving you notice, in most cases you should be notified and asked for consent. Normally your dedicated firewall software asks whether to allow traffic or handles it on its own depending your settings for it. Here is a small list of games asking for internet access:

Pendragon
The Dark Crystal - Age of Resistance Tactics
Nanotale
Radical Relocation Had a pop-up of Windows firewall in addition to Comodo ... Strange since the Windows one should not be running, it is shown as being deactivated ... Windows 10 ...
Game Dec [Demo]
The Witcher 3
Dorfromantik
Underrail
Beyond a Steel Sky
Dead Synchronicity Tomorrow Comes Today
Hearts of Iron III
...

and many more. Why? In some cases, Dead Synchronicity, Beyond a Steel Sky, Nanotale, nado, I asked myself the very same question. In some I do know the answer: Unity Analytics - a pest ... and in some others at least for MP, though maybe also other purposes. I never scanned and analyzed traffic. I bet there are other community members having done this work and published what they found, I think I have seen such being discussed here ... Sorry for not being able to provide a link ... :)

I do both.
It's kind of unnecessary, but at least with games that use ScummVM and Dosbox you can use game files as is, if you have those programs installed otherwise, but GOG installer can be useful for having some special settings preconfigured. Not to my knowledge, no. They should work 100% offline even if you turn off all net services. Of course some DLCs are available only through Galaxy, which is another thing. They work just like old CD-ROMs, and in fact in the case of some good old games they are actually emulating optical discs. GOG installers should work on any compatible computer always and everywhere, that's what DRM-free means. I haven't seen any GOG installers that would work otherwise.

In the unlikely case that some GOG installer would refuse to work, there are third party tools that can extract the game data from them. You can also use those if you are using some unsupported OS.

http://constexpr.org/innoextract/ All you need is whatever files the game has and a script that tells where to put those files on your computer. It's not that complicated, it's much more complicated to create online installers and clients.

You backup the offline installer itself. No. They work offline by design. Yes they will continue to work offline. Simple test - reinstall Windows / buy a new computer and completely disconnect your Internet connection. They will work (and without any client or need to log into GOG) whilst DRM'd versions on Steam / Uplay, etc do not. They are created by GOG and once downloaded do not need any server. The user generally doesn't need to create them, that's done at GOG's end. I'm sure everyone has some pieces of utility software on their computer like 7zip, CPU-Z, MSI Afterburner or VLC (and probably the web browser you're using). You download those installers, run them and they put the program on the disc, create a Start Menu shortcut, etc? GOG installers work the same, only for games.

@Ryan333 said it pretty right.

On top of that, how much storage space do you want to waste, and how quick do you want to copy your backups?

Offline Installers are compressed and add up to much less storage needed than an uncompressed game install folder.
They are also quicker to copy, as big files always are compared to many many small files.
And if you ever need to create an exception in your AV I'd be surprised ... never happened to me for over 1200 games, using MS AV. But then I just copy the installers (EXE, BIN, SH, ZIP files). A game folder has many more types, some of which may hold things up with your AV ... though you could just except the install folder and destination folder in your AV.

GOG is about DRM-Free. It wouldn't be DRM-Free if you needed to phone home to GOG etc on the web when installing.

Just making sure, so I can backup up to discs right? Also, lets say the witcher had 4 parts with two of the bin files being 3.9 GBs, and my one disc can hold about 4.32 GBs. Can I put one bin file on one disc and the other bin on a separate disc, then when want to install, I use one disc, copy, and then use other disc and copy the other bin file?

So would an example include Settlers 3 with the serial number that is bypassed? So, again just double checking, backuping up the offline installers are safe, right?

Yes, a bin file per dvd should work. It theoretically should ask you to put in disc 2 when needed. I havn't actually tested this because i bulk install, so copy discs to hdd first, then install. Also i use bluray to backup not dvds. I wouldnt recomend dvds because they are easily scratched. Blurays have scratch resistant coating on standard discs. You dont need to get special archive grade discs to get scratch resistant coating. Also burn slow. The laser can't maintain constant writing power. Slow speed also means less vibration which leads to faster read speeds. Good idea to verify too.

Ok, thank you everyone for the information you have provided me with to have a better understanding of how all of this works! May you all have a wonderful day and week!

Diablo and Warcraft 2 are two examples I can immediately think of. They add a Windows firewall rule for the legacy Battle.Net server. That's only needed for their multi-player component, though, and the single-player portion still works without the added firewall rule.

Yes, "offline installers" are just that. They work offline, no Internet connection required. But....