Summary
If you have installed IMSS 9.1 build 1172, you may encounter an issue where you are unable to update the AntiSpam Engine and any attempt to do so fails with the error message:
[Antispam Engine] Pattern Update: Unable to verify the downloaded file: 0The downloaded anti-spam engine is corrupt.
[Antispam Engine] Pattern Update: Unable to verify the downloaded file: 0The downloaded anti-spam engine is corrupt.
Details
This issue is resolved by installing IMSS 9.1 Patch 1 build 1323, which can be downloaded from the download center at the link below:
https://files.trendmicro.com/products/interscan/imss_91_lx64_en_patch1_B1323.tar.gz
https://files.trendmicro.com/products/interscan/imss_91_lx64_en_patch1_B1323.tar.gz