Sensen DOS stuns all surrounding enemies. It's effective against all enemies except those with helmets, such as Elite Enforcers, Recoversion Leapers and the Mourners in Episode 8. Sensen DOS is especially useful against Mourners, as it cancels their invisibility and exposes them to attack.
"Sensen DOS" is reference to a Denial of Service attack, a well-known attack method used by cyber criminals to take down servers and websites by flooding them with connection requests and other information. The affected system slows down to a crawl or crashes, becoming unable to perform its function.