When you're an entrepreneur, getting acquired is always a possibility and one of the down-the-road exit strategies you keep in the back of your mind. But in high tech, the pace of big companies buying small firms has exploded to a degree that might surprise you. Try 2,357 private tech firms bought in 2012 for a total of about $84 billion, according to private company market analyst PrivCo.

PrivCo looked at the top 100 acquiring companies. You might be surprised at who's gobbling up start-ups the fastest. Here are the top five in order of the number of acquisitions, according to PrivCo:

  1. Facebook
  2. Google
  3. Groupon
  4. Twitter
  5. Cisco

That's right, Apple's not in the top five. Neither is Microsoft or Oracle or HP. But privately held Twitter is.

More important, the pace of acquisitions is feverish. Why? The answer is "defense," according to PrivCo CEO Sam Hamadeh. There are two things tech-related companies--and that includes private equity firms like Thoma Bravo, which was the most active acquirer in the private equity field--are trying to achieve.

Raising the body count

These firms need more talent, and the race for engineers and designers has probably never been hotter. Look at the email trail in the employee suit alleging that Apple, Adobe, Google, Intel, and others had entered into "do not poach" agreements. (Six big tech companies entered a DOJ settlement over the allegations in 2010.)

When you can't get the people you want through direct hires, so-called acqui-hiring, or buying a company simply to bring the employees and expertise on board, has become the new normal in Silicon Valley. And given the cash war chests in place, some of the giants may acqui-hire not for planned projects but simply to keep key human resources out of the hands of competitors.

Was someone innovating? 'Cause it wasn't us

The other reason for the massive binge is the quest to find the Next Big Thing, which probably won't come out of the bowels of a very large company. I recently wrote about how an IPO can kill innovation. Notice that of the top five acquiring companies, only one is private. And I'd argue that because of the pressure to pump up revenue, Twitter probably has had to shift the way it does business and become more staid.

This is another two-pronged activity. First, if there's something hot, a big company might want to incorporate the technology into what it does. Apple is an example, as much of the groundbreaking work in mobile technology and interfaces it has displayed came from companies it acquired.

But there's the darker part, as well--keeping potential market upstarts and disrupters at bay. As Hamadeh put it to me, "As soon as buyers like Facebook [the No. 1 most active buyer in 2012, and it wasn't even public for the first four months of 2012] and Twitter [and now Google] see any traction from a new app or piece of software, they buy it and then kill it. It has become easier than trying to compete with something totally new."

What's the future?

All signs seem to indicate that things will get only hotter in 2013. "High yield debt and leveraged loans are at their lowest rates," Hamadeh says. "That drives M&A. The junk bond index is at a historic low. I saw one just under 4 percent. It's stunning that a leveraged buyout could issue a junk bond [at that rate] and investors are so stretched for yield that they took it." Even 6 percent for a risky investment is very low.

Plus, there's all that cash that companies have on the balance sheet. Interest rates are so low that the capital offers little return parked in a bank. So the big companies are investing via acquisition.

"Unless something changes, 2013 is on track to be even stronger in acquisitions of private companies," he says.