Editors' pick: Originally published Dec. 15.

Shares of Yahoo! (YHOO) were lower by less than 4% in late morning trading on Thursday, despite the company announcing on Wednesday that it had uncovered a security breach from 2013 that involves 1 billion accounts. This cyber-attack is separate from the previously disclosed 2014 hack of 500 million accounts.

Markets aren't reacting more strongly to the breach because people are starting to realize that all companies are getting compromised, so it's not a Yahoo!-specific problem, co-founder of cybersecurity technology company Crowdstrike Dmitri Alperovitch said on CNBC's "Squawk on the Street" on Thursday. 

"There are only two types of organizations: those that know that they've been hacked and those that don't yet know," he said. "But they've all been hacked."

All of these companies are facing "incredibly sophisticated targeted attacks" from nation states and organized criminal groups, Alperovitch said. That's why we need to be taking cybersecurity seriously. 

Some are questioning why Yahoo! took so long to discover the breach. 

While we don't know when exactly the company uncovered the hack, it's not uncommon for attackers to be in networks for months or years before being discovered, he noted. "So this is actually pretty routine. It really underscores that if you don't have full visibility to what's happening in your network, if you don't use next-generation host base technology to identify what's going on in your computers, you'll be breached for many, many years and not know that your data is just going out the door continuously."