Due to the nature of DLL injection—a technique also used by malware—many antivirus programs will flag the Extreme Injector as a "Trojan" or "Potentially Unwanted Program" (PUP). If downloading from the official GitHub, these are typically false positives, but you should always exercise caution when running such tools. , or do you need help with troubleshooting a failed injection? master131/ExtremeInjector - GitHub
Used as intended on non-critical processes, no. But injecting into system processes can cause instability or crashes.