You may receive a Changed Program alert if a program has been changed or updated since it was last used.

If the program has not been updated to your knowledge, it may have been updated automatically in the background without showing a notification but it is possible that the program has been affected by an exploit or Malware.

To ensure that the program is not infected and is not malicious, scan the location of the program (as shown on the ZoneAlarm Alert window) with your AntiVirus scanner. In the majority of cases, the program was just updated quietly in the background without the user's knowledge.