With all respect moose;

I think you may over estimate the vulnerability of transaction based systems. They profile every entry, and code (any form of malware) sent to the system will not fit the profile. There should be only be 2 types of entry paths to the system, transaction and maintenance, and the technology exists to protect those systems from all but trusted internal users.

General office computers or “unprotected input” are another situation, but no engineer would implement a “secure” system on a bunch of networked office computers.

Communication systems may be targets but modern comm components are very reliable and quick to recover. A system that has any sense of security and availability will not have a single point of failure other than power or external infrastructure.

I am not quick to claim "conspiracy" nor am I claiming to know what happened yesterday. But if the TSX is subject to a virus, it would indicate a very poorly designed system.