It’s official. Cybersecurity venture capital funding hit a record $5.3 billion in 2018, according to Strategic Cyber Ventures.

This is 20 percent higher than the $4.4 billion companies raised in 2017 and 81 percent higher than in 2016.

But, as the VC firm warns, “this rate of investment is not sustainable.” There are likely many security “zombies” that initially raised big rounds but are now experiencing slowed growth. These companies “are being propped up by existing investors that will eventually grow weary of keeping them alive.”

While the total funding grew year over year, the total number of 2018 deals remained nearly the same with the average investment coming in at $15.8 million. Some of these mega-deal winners — like Tanium, which raised $100 million and CrowdStrike, which closed a $200 million Series E — are expected to go public this year. But things like the U.S. government shutdown and trade wars with China may make the public equity markets not as attractive in 2019, Strategic Cyber Ventures notes.

The mergers and acquisitions market remained strong but short of the five-year highs in 2015. Some of the big M&A deals in 2018: Cisco acquired Duo Security for $2.4 billion, Blackberry bought Cylance for $1.4 billion, and AT&T reportedly payed $600 million for AlienVault.

Last year also saw private equity firms getting into the security market, with Thoma Bravo alone spending billions to acquire security companies. It acquired Barracuda Networks for $1.6 billion, Veracode from Broadcom for $950 million, and Centrify for a reported $400 million. Thoma Bravo also approached Symantec in November about acquiring the software company.

And finally, 2018 proved to be another strong year for initial public offerings with four “significant” IPOs raising about $1.4 billion. These include Avast Software ($811 million), Tenable ($251 million), Zscaler ($192 million), and Carbon Black ($152 million).