Internet-Security.com TCP port 990 details

TCP port 990 is used by FTPS in implicit mode (FTP over TLS/SSL with an immediately encrypted control connection; data channel typically on 989).
Real-world servers supporting implicit FTPS on 990 include Microsoft IIS FTP service, FileZilla Server, vsftpd, ProFTPD (with mod_tls), Progress WS_FTP Server, SolarWinds Serv-U, Globalscape EFT (Fortra), and Progress MOVEit Transfer.
Many storage/MFT devices also expose FTPS on 990, such as Synology NAS (DSM FTP service) and QNAP NAS when implicit FTPS is enabled.
Security note: Port 990 is commonly scanned for FTPS services and targeted for brute‑force and TLS/FTP misconfiguration attacks, and past vulnerabilities in FTPS server products (e.g., Serv-U, WS_FTP Server) have been exploited when Internet-exposed.

TCP 990