NEW YORK (MainStreet) — Your retirement security likely depends on that mysterious investment machine known as the 401(k). There are a lot of moving parts in that thing, and most of us have only a vague idea of how it works. Somehow, we put money in and the machine invests in tiny slivers of ownership and loans of hundreds of companies. Hopefully, great companies such as Apple, Netflix, Google and Bristol-Myers Squibb.

But some investors may be surprised to learn that their 401(k) might also be making bets on the likes of SpaceX, Zynga, Snapchat, Airbnb, Uber and Pinterest. Big players in the retirement plan industry — such as T. Rowe Price, Fidelity and BlackRock — have all bought into tech startups through special syndicate deals that allow them exclusive access to such privately held companies.

Should you be worried or thrilled? Peter Fisher, managing partner of Human Investing, based in a suburb of Portland, Ore., says perhaps a little of both.

"The participant, hopefully, should be investing in something that is what they thought they were investing in,” Fisher says. “So if you're going to put a fund that has a bunch of startup stuff or venture capital or non-publicly traded stuff or thinly traded stuff in your 'safe box' — shame on you. But if this is something that is in a specialty category, I think it could be a huge opportunity for some people that don't have access to that sort of thing. As long as it's communicated the right way."

Though Fisher's firm is a passive investment advocate, preferring index funds to actively managed funds, he thinks there is a place for such portfolio sweeteners: "Do I think these types of investments should be considered? Certainly. Absolutely."

Joe Lucey, a financial planner in St. Louis Park, Minn., says it’s often not the particular stock that’s the problem, but how much of it you own.

"The ability to own some of the startup companies is probably not something that I'd have a problem with, but on the other hand oftentimes we'll see employees that have company stock in publicly traded companies — everything from Target to 3M — where all of a sudden they end up having all of one company's stock in their 401(k),” Lucey says. “So whether or not it's a startup company or a Fortune 1000 company, if [investors] aren't well diversified, that can always cause problems or concerns."

A sprinkling of startup exposure in your retirement plan

As for the Uber holdings in your 401(k), they are likely to be a very thin slice. Fidelity says the crowd-sourced taxi service makes up less than a 1% share of its mutual funds. But don’t think the shares are held in just the company’s Contrafund or other tech-leaning mutual funds; Uber was the biggest winner in the Fidelity Blue Chip Growth Fund during the last quarter of 2014 — yes, the Blue Chip fund. Blue chips are the benchmark of quality on Wall Street, represented by the 30 stocks of the Dow Jones Industrial Average.

But Uber is far from a blue chip stock. Fidelity says it’s an “out of benchmark” holding.

“Not all of the names we invest in are blue-chip companies — some are companies that we believe have blue-chip potential down the road,” says Fidelity’s quarterly fund review.

Transparency

And there’s the challenge: how to know exactly what your 401(k) is investing in. The mutual fund names alone obviously provide few clues. And mutual funds can allocate up to 15% of their holdings in private companies and other illiquid securities. Investors need to uncover the facts and see where their retirement money is really being invested.

Lucey admits the online tools available to the average 401(k) investor often don't drill down to that level of detail. Instead, he recommends 401(k) investors take the initiative to find out what the specific holdings are in their retirement plan — by asking the plan administrator. He suspects few consumers will make such an effort.

Fisher’s firm uses Morningstar technology, integrated with a participant's 401(k) account, to provide just that kind of investment transparency.

"With a push of a button, they can run a cross-section report on all their holdings," Fisher says. "They can see, 'OK, I own 2.12% of Apple across the three mutual funds that I own.’" The firm uses the analytic tools to advise 401(k) participants for company clients who sign up for the service.

Though minor holdings in tech start-up stocks may not be a problem for the great majority of retirement investors, Lucey says there is one challenge many saving-oriented consumers face.

"A lot of consumers are taking far more risk in their 401(k)s,” he says.

Last year would be a good example. The S&P 500 was up some 13%, so those investors that are focusing their portfolio in the top 500 S&P indices may think they get 500 companies that represent a fully diversified portfolio, but are exposing themselves to unrecognized risk by not diversifying across all asset classes, Lucey said, by adding some international investments, bonds and what have you. In short, having exposure to Uber — or Meerkat, for that matter — is not terrible as long as your holdings are hedged accordingly.

Keeping priorities straight

Still, investors suffer a dangerous sort of amnesia of losses in past years and are inclined to go bold.

"Nobody liked what their portfolios did in 2008, [but] we're seeing clients coming into our office back to the level of risk that they were at right before the last correction," Lucey said.

And Human Investing’s Fisher adds the highest priority investors should be most concerned with:

"The 401(k) investor should worry about, first and foremost, whether they're doing their part in creating a plan to defer enough for retirement, based on the life they want to live at some point down the road,” he says. 

— Hal M. Bundrick is a Certified Financial Planner and contributor to MainStreet. Follow him on Twitter: @HalMBundrick