An ECS file is a data backup file created by Sony Ericsson mobile phones. It stores a copy of user’s data as backup in case recovery is required for restoring the stored data. ECS files are saved as compressed ZIP archives to reduce the disc space utilization. This also makes it easy for transferring data over low speed internet connections.
ECS File Format - More Information
ECS files are saved as compressed ZIP archives. It can be opened with any standard unzipping program like WinZip and WinRAR. For this, rename the file extension from .ecs to .zip and extract the contents with WinZip.