That long string of letters and numbers is the hexadecimal representation of the package's checksum, calculated when the package is uploaded via Casper Admin (and can be manually calculated if uploaded by other means, by right-clicking on a package and selecting "Calculate Checksum").
The checksum uses an algorithm called "md5" to calculate a value that, for the most part, uniquely represents the content of the file. If a single bit changes in the file, the checksum will be very different. The Casper suite can use this checksum to verify that a package being deployed on a machine via Policy or other means is in the exact same condition that it was when it was uploaded - i.e., there are no corruptions. This is done by recalculating the checksum on the client and comparing it to the one stored in Casper Admin.
Main points to take away:
If the checksum says "None", no checksum has been calculated, and Casper won't attempt to verify a package when deploying it
If the checksum has a long string, then Casper will verify a package before deployment, and refuse to install it if the verification fails
If you manually (e.g. upload to a share without using Casper Admin) replace a package (e.g. an update) that had previously has a checksum calculated, you will need to get Casper Admin to recalculate the checksum by right-clicking the file, and selecting "Calculate checksum", otherwise package verifications will fail and it won't get deployed
I hope this helps
