Once the virus has been extracted and isolated, it is easy enough for Hiro to write a new program called SnowScan. SnowScan is a piece of medicine. That is, it is code that protects Hiro's system—both his hardware and, as Lagos would put it, his bioware—from the digital Snow Crash virus. Once Hiro has installed it in his system, it will constantly scan the information coming in from outside, looking for data that matches the contents of the scroll. If it notices such information, it will block it.