Ness didn't have to hack Capone's PC.
Legwork worked in the 1940s because the criminals were on the same level. Your mobsters were generally within reach because to remain in control, they had to remain in communication range, which was usually in person.
Today, criminals can sit in Afghanistan and manage loose groupings of local networks very effectively. Drug cartels operate from Mexico. Criminals have the same capabilities that states had in the 1940s. Did we expect legwork to break codes? There is always legwork involved, but we were using SIGINT to get good information even then.
And bear in mind that we used to have the option of the wiretap, even in the days of Capone. Useless now with encrypted communications.