What is a .iso file?

About the format

An .iso file is a disc image: a byte-exact copy of an optical disc's file system, kept alive decades past the optical disc itself because it's the standard way to ship operating systems and large software. Windows installation media, Linux distributions, and Microsoft's own download tools all produce ISOs. Since Windows 8, Explorer mounts an ISO natively — double-click and it appears as a virtual DVD drive with a letter; right-click → Eject unmounts it. To make bootable USB installation media from an ISO, a writer tool (Rufus is the de-facto standard, or Microsoft's Media Creation Tool for Windows itself) copies it with the right boot structures — just copying the .iso file onto a USB stick does not make it bootable, the most common ISO mistake. Security-wise an ISO is a container like a ZIP, and attackers have used that: ISO email attachments historically dodged the mark-of-the-web on their contents. The judgement, as ever, applies to what's inside — and to downloading OS images only from the vendor.

How to open a .iso file

Is a .iso file dangerous?

A container. Historically used in email to smuggle executables past filters — an unsolicited ISO attachment is a red flag.

Related file types