Symantec's security software often comes bundled with personal computers. As a result, the company has suffered as consumers use mobile devices more than traditional computers. While Norton remains profitable, its sales have been falling.
"(Norton) had been declining with the declines in PC market share. This acquisition brings $660 million in revenue to the consumer business and returns it to longer sustainable growth," Symantec Chief Executive Greg Clark said in an interview.
Reuters was first to report earlier on Sunday that Symantec was in the lead to acquire LifeLock.
Symantec's purchase of LifeLock is in line with its efforts to diversify its offerings. In August, it bought Blue Coat, which helps firms maintain security over the internet, in a $4.65 billion deal. Clark previously held the top job at Blue Coat, and made the switch after the deal closed.
Based in Tempe, Arizona, LifeLock offers services such as monitoring new account openings and credit-related applications in order to alert consumers about unauthorized use of their identity. It also works with government agencies, merchants and creditors to remediate the impact of identity theft.
Fran Rosch, executive vice president of Norton Business Unit, said that Symantec had dabbled in identity security but had nowhere near Lifelock's 4.4 million members.
"We had to extend our value proposition. It was a no brainer for us to get back to growth," Rosch said.
Symantec expects to finance the transaction with cash on balance sheet and $750 million of new debt.
The Mountain View, California-based company has been moving away from what is sees as more commoditized services, selling its data storage business Veritas in January to private-equity firm Carlyle Group for $7.4 billion. Technology-focused firm Silver Lake Partners has also made a $1 billion investment in the company in two parts this year.
Symantec said the LifeLock deal is not expected to have a material impact on its financial results next year, and reaffirmed its fiscal year 2017 and 2018 guidance. The deal also represents a victory for activist hedge fund Elliott Management Corp, which had pushed LifeLock to explore its options.