Yahoo! Inc.'s disclosure of a billion-account data breach—its second major breach revelation in three months—will increase the likelihood of regulators taking public data security enforcement action, privacy and security professionals said December 15.

Edward J. McAndrew, a cybersecurity partner at Ballard Spahr LLP in Philadelphia, told Bloomberg BNA that it would be "very surprising if Yahoo's data security practices did not attract the attention of various regulators here and abroad, beginning with the Federal Trade Commission."

The FTC, state attorneys general and international privacy regulators will want to "investigate how Yahoo failed to secure the personal data of at least 1.5 billion" accounts over such a long period of time, McAndrew said.

Yahoo announced Dec. 14 that more than 1 billion user accounts may have been affected in a 2013 data breach incident. This data breach is in addition to a 2014 breach incident the company disclosed in September that may have compromised at least 500 million user accounts.

Yahoo is the ninth largest public internet media company in the world with approximately $39 billion in market capitalization, Bloomberg data show. Verizon Communications Inc. agreed to buy Yahoo for $4.8 billion, in a deal scheduled to conclude in early 2017. According to a December 15 Bloomberg Technology report, Verizon is exploring a price cut or possible exit from the pending acquisition.