Microsoft deprecated support for SHA-1 hashes signed after 2016-01-01: https://technet.microsoft.com/library/security/3123479?f=255&MSPPError=-2147217396
Splunk 6.3.3 has such a hash, so IE doesn't like it.
Future releases of Splunk will use another hash. Please download with another browser as a workaround for 6.3.3. This problem should eventually show up on the known issues documentation.
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