Amnesiac Virus

The Amnesiac Virus is a computer virus developed many thousands of years prior to the The Xahian Crusade by unknown parties and designed to attack AI and computer storage. Its attack mode was to wipe clean memory storage and disable AI encephalisation, destroying progress in the AI gaining sentience-level intelligence. If it were limited to networked machines, then it could conceivably be isolated and destroyed, but at some point in its deployment, it was altered into a broadcast signal, enabling it to corrupt computer systems from a substantial distance away. The signal is remarkably pure, and has swept through the entirety of Known Space, re-emerging on numerous occasions.
It's origins are unknown; speculation puts it at either a rogue AI, or having origins outside of human space, by unknown beings. Some blame was given to groups seeking to rebel against the post-scarcity luxury of the times, but modern scholars doubt that such groups would have the capabilities to create something this pervasive and destructive. Whatever its origins, it was devastating to human society, which at the time relied extensively on AI and robotic labour to support its civilisation.