It would be irresponsible to ignore the risks. OS X 10.11 El Capitan . The last patch was released in 2018. If you connect an El Capitan machine to the internet:
The safest way to obtain OS X 10.11 is through official Apple channels to ensure the integrity of the installer. 10.11 mac os download
Double-click InstallMacOSX.dmg to mount the disk image. It would be irresponsible to ignore the risks