: It includes cumulative security patches and vulnerability fixes (PSIRT advisories) integrated throughout the 15.9(3)M train, providing a more secure environment than older 15.7 or 15.8 versions. Modern Feature Support
Surprisingly, "better" code sometimes removes deprecated features. If you rely on or L2TP (non-IPsec) , this image deletes support. Similarly, some third-party DSL chipsets on the 800 series behave poorly with the 15.9 train compared to the 15.4 train. c800universalk9mzspa1593m10bin better
To provide "helpful content" for the Cisco IOS image c800universalk9-mz.SPA.159-3.M10.bin : It includes cumulative security patches and vulnerability