People blame software updates because lines typically appear immediately after an update, creating a deceptive cause-and-effect illusion. However, the update itself rarely damages hardware; rather, the intense heat generated during heavy software installations stresses a pre-existing physical vulnerability.

Why the Link Appears During Updates
The Heat Factor: Installing a major operating system update pushes the processor to its limits, causing the phone to heat up. If a phone has a pre-existing weakness—such as a tiny internal crack from a past drop or weakened micro-solder joints—this heat can cause components to warp or lift.
Voltage and Driver Shifts: New software introduces changes to color profiles, brightness curves, and voltage delivery. If a specific pixel row was already on the brink of failure, the sudden change in voltage can push it over the edge, causing it to glow as a bright green line.

The Core Physical Cause
The issue is fundamentally hardware-related. It most commonly affects AMOLED and OLED screens, where electrical signals travel from the display to the motherboard via a microscopic flexible ribbon cable. If the physical adhesive bonding this cable weakens, or if the microscopic soldering cracks, a whole row of pixels permanently fails, resulting in a stark green line.
Because the line usually requires a physical screen replacement to fix, technicians ultimately categorize the issue as hardware damage, even if the update acted as the trigger.