[kbirkeland]

Advertising the longest generally-accepted prefix is more of a BGP hijack defense than a DDoS defense. Longest prefix always wins in IP forwarding, so advertising the longest prefix enforces that the best path to you is (usually) selected by local preference or AS path length.

[dylz]

I see it used in DDoS defense by "hijacking" the traffic of the /32. The standard unprotected provider gets hit and the mitigation provider announces a more specific /48 then tunnels the traffic back out of band