iMacros can calculate the checksum of a downloaded file and compare it with the value of the CHECKSUM parameter. This is very useful to verify the file downloads are not corrupted, or worse, have been infected by a virus or Trojan horse (e. g. via a hacked server).
How to calculate the checksum: Just run the macro with an arbitrary value for the checksum and you get the correct checksum directly from the iMacros error message: Checksum of downloaded file be90867e72c1fd00022597063f123251 doesn't match specified
Alternative: There are many tools for calculating a file checksum. For example you can calculate the MD5 checksum with the Microsoft File Checksum Integrity Verifier "fciv" tool:
fciv -md5 filename.exe
or if you want to save the output to a file:
fciv -md5 filename.exe > text.txt
The resulting iMacros ONDOWNLOAD command is:
ONDOWNLOAD FOLDER=* FILE=* WAIT=YES CHECKSUM=MD5:abe871f602c4fdfedc93404d5f7df877