"Hackers Compromised the Trump Organization 4 Years Ago—and the Company Never Noticed... In 2013, a hacker (or hackers) apparently obtained access to the Trump Organization’s domain registration account and created at least 250 website subdomains that cybersecurity experts refer to as “shadow” subdomains. Each one of these shadow Trump subdomains pointed to a Russian IP address, meaning that they were hosted at these Russian addresses... The subdomains and their associated Russian IP addresses have repeatedly been linked to possible malware campaigns, having been flagged in well-known research databases as potentially associated with malware. The vast majority of the shadow subdomains remained active until this week, indicating that the Trump Organization had taken no steps to disable them.... For each of over a hundred of these ... domains, the intruder created two shadow subdomains,... ...For many but not all of the ... subdomains, according to the VirusTotal listings, Kaspersky, the Russian antivirus company, detected a possible association with malware... 'It’s telling that Kaspersky detected [this malware], while others didn’t,' ...That could be a measure of the malware’s sophistication..." http://www.motherjones.com/politics...on-4-years-ago-and-the-company-never-noticed/
I expect that most hacks go unnoticed. There would be little way to tell until someone found the results.