A virus hid in the part of a disk computers checked first
Brain spread through floppy disks by infecting the boot sector—a small area the computer reads when starting up. If someone used an infected disk, the virus could copy itself onto other disks, turning routine file-sharing into a route for infection. Its authors reportedly intended it to identify unauthorized copies of their medical software, not to cause widespread damage.
The brothers’ contact details embedded in the code made the program unusually traceable. But identifying its authors did not remove it from infected disks or stop it from circulating. A virus could travel wherever the disks went, including beyond the original software’s users.
The response was to inspect the disks
Brain’s spread helped prompt the development of commercial antivirus software in 1987. The basic challenge was to detect code that had been inserted into places a computer used automatically. Antivirus tools could examine disks for recognizable traces of malicious code and help users identify or remove infections.
That marked a shift in computing: a floppy disk was no longer just a container for a program or document. It could also carry instructions that ran before the computer was ready for ordinary use. The same portability that made disks useful for sharing software made them a practical way to spread viruses—and made security software a new part of personal computing.
