There has yet to be a government that is immune to cybersecurity threats. The U.S. has some of the most developed cyber-practices in the world, as does Canada, as Mr. Waterhouse pointed out. It is also home to the companies with the most mature security practices in the world. Even so, hacks may still happen. So we're up against a race.
The Internet is a very complex system with a lot of people contributing to it. Everything is tied together. Systems and networks change or contain hundreds of thousands of individual hardware and software components and thousands of lines of code. Every time code is updated, which may happen multiple times a day, new vulnerabilities may be introduced. There will always be unknown unknowns and the only way to uncover these unknown unknowns is to invite good hackers to test the system. Even with systems that have been proven to be very secure, changes may happen overnight either because of an internal or external change, and vulnerabilities may arise.