Some programs that have mining functions may be regarded as malware by security softwares because some Trojans mining in the background.
HashFish is legit mining software and is verified by VirusTotal and passed AV-TEST, AV-C, VB100, which do not harm to your device.
If HashFish is regarded as a malware by Windows Defender in Windows 7/8/8.1/10, please set HashFish as an exclusion in security software as mentioned as flow:
Note: Default installation path of HashFish in Windows 7/8/8.1/10 is: C:\Users\User's name\AppData\Roaming\HashFish
1. Enter Windows Defender center, click the button as shown
2. Click "Virus and threat protection settings".
3. Find "Exclusion", click "Add or remove exclusions", select "Folder", find the path (example: C:\Users\user's name\AppData\Roaming\HashFish) and confirm.
4. Now enjoy your mining.