Is Rainer a virus?
Rainer may be detected as a virus by your antivirus but that is a false positive due to the dll injecting code to Roblox and de main exe file being obfuscated.
How do I disable Windows Defender?
Rainer is getting deleted, all the time automatically!!!
Check if your antivirus is off, if it still gets deleted then you might have +1 antivirus, just turn all of them off, (if you think that you don't have antivirus then you prob have windows defender, check How do I disable Windows Defender? wich is the faq before this one)
Rainer says that I have to inject before executing...
Well, this means you have to click the inject button before trying to execute something! An if you already did that but it still says that, download this: https://www.microsoft.com/en-us/download/details.aspx?id=53840
When I click on the website it redirects me to other random sites...
That is ads, just close them, never download anything from those ads, the only external website where you should install something from Rainer is FileDM
Why the Rainer website has ads and why Rainer has a key system?
Sadly not everything in this world is free, and we need to pay to keep the Rainer servers up + be able to update it, the ads on the website, the installer and the key system give us the money that we need to pay for all of that
When i inject Rainer my Roblox close / crash.
Reinstall roblox, if the problem continues then delete the roblox folder (don't just uninstall it) and then install roblox back!