To ensure an ISO is genuine and untouched, you should verify its checksum (SHA-1). For official MSDN images, you can compare your file's hash using tools like PowerShell Licensing:
Pre-cracked ISOs frequently contain hidden trojans, keyloggers, or ransomware. These threats install themselves at the root level of the operating system, making them incredibly difficult for standard antivirus software to detect.
Windows 7 is already vulnerable as an unsupported OS; using a cracked version prevents you from receiving even the most critical legacy updates. How to Safely Obtain and Use Windows 7