Of the total breaches, nearly one-third involved CEO spear phishing, the ITRC pointed out. FBI officials recently issued a warning of a dramatic rise in business email compromises, in which perpetrators target internal employees with access to financial or sensitive employee data by impersonating executives, trusted individuals or vendors.

Another threat to organizations is ransomware.

The Sunnyvale, Calif.-based security firm Proofpoint's analysis of first quarter 2016 threats and trends revealed ransomware vaulted into the top ranks of cybercriminals' most preferred malware. Nearly one-quarter of document attachment-based email attacks in the first quarter featured the new Locky ransomware.

The ransomware threat also caught the attention of Congress. Rep. Michael C. Burgess (R-Texas) said ransomware criminals should be "shot at sunrise" at an encryption hearing before a House subcommittee on Tuesday.

"The comment that Mr. Burgess has made deserves special mention, especially in the light of a considerable increase in ransomware strikes in recent times and the need for strong internet security measures," the Clifton, N.J.-based Comodo wrote in a blog.

The cybersecurity firm added, "Ransomware, like other malware, can infect a system or a network without anyone getting a hint about it. Those affected would be forced to pay a ransom to get them out of this plight."

LinkedIn also responded to reports of a security issue with an emailed letter to members.

"On May 17, 2016, we became aware that data stolen from LinkedIn in 2012 was being made available online. This was not a new security breach or hack. We took immediate steps to invalidate the passwords of all LinkedIn accounts that we believed might be at risk. These were accounts created prior to the 2012 breach that had not reset their passwords since that breach," the company wrote.

LinkedIn said the information involved included member email addresses, hashed passwords and LinkedIn member IDs (an internal identifier LinkedIn assigns to each member profile) from 2012.

"We invalidated passwords of all LinkedIn accounts created prior to the 2012 breach that had not reset their passwords since that breach," LinkedIn wrote. "In addition, we are using automated tools to attempt to identify and block any suspicious activity that might occur on LinkedIn accounts. We are also actively engaging with law enforcement authorities."

LinkedIn said it has taken significant steps to strengthen account security since 2012. For example, it now uses salted hashes (random data used as an extra input) to store passwords and enable additional account security by offering members the option to use two-step verification.

"We have several dedicated teams working diligently to ensure that the information members entrust to LinkedIn remains secure," the letter said.