If you downloaded the file from a legitimate Cisco portal, you will have an MD5 or SHA256 checksum. Always verify your binary:

Searching the web directly for "c3725-adventerprisek9-mz.124-15.t5.bin download" often leads to a variety of file-sharing forums, unverified cloud storage folders, and questionable tech blogs. Relying on these sources introduces significant operational and legal dangers. 1. Malware and Supply Chain Attacks

The official Cisco website is the recommended source for downloading IOS images. However, you'll need a valid Cisco account to access the software.