We're back for the final installment of our series examining the three stocks in the Motley Fool Rule Breakers portfolio that have more than doubled in two years.

In previous articles, we looked under the hood of Vertex Pharmaceuticals, which has more than tripled, and NYSE Group, which is a four-bagger. Today, our subject is Akamai Technologies (NASDAQ:AKAM), which I picked for our May 2005 issue and which is up more than 320% since then.

Why I bought
Akamai was my first subject as a Fool writer in December 2003. Though the company was still unprofitable at the time, sales growth was accelerating and gross margin was expanding rapidly. Investors had noticed; the stock was a five-bagger that year alone.

But 2004 wouldn't be as kind. Though still a market-beater, Akamai's stock leveled off. I thought that was unwarranted. Profits and cash flow had continued to blossom, after all. Meanwhile, Akamai was still the dominant content delivery network with more than 60% of the market.

Besides, thanks to Microsoft (NASDAQ:MSFT) with downloadable system updates and Apple (NASDAQ:AAPL) with iTunes, Akamai's network had become crucial. I said as much in the buy report:

You probably arrived at Fool.com through one of Akamai's 15,000+ EdgePlatform servers, a computer positioned close to you that houses some of our content and, like your faithful postman, delivers it on the quick and cheap. That may seem simplistic. Yet with the growth of the Web and the increasing population of netizens who download music, pictures, videos, and games and tune in to streamed media, the once-flailing refugee of the dot-com meltdown has suddenly become more important than ever.

There was also an attractive valuation and a deal to acquire its major rival of the moment, Speedera, which would retire potentially damaging litigation. All signs pointed toward higher highs for the stock. By that October, Akamai, up more than 35%, was making my wish for big portfolio gains come true.

Why I'm holding on
But sales and earnings continued to accelerate. Today, in spite of some of the world's worst reporting, Akamai's stock story as compelling as it ever was. And a recent deal for Nine Systems appears to have enhanced an already impressive portfolio of services for Akamai's 2,000 regular clients who create and distribute content via the Web.

That's not enough for some critics. They point out that there's plenty of potential competition from Web titans with an interest in controlling the digital tollways they own. Google (NASDAQ:GOOG) and Yahoo! (NASDAQ:YHOO) come to mind.

Then there's pure-play content delivery network rivals, including Limelight and InterNAP (NASDAQ:INAP), which recently acquired VitalStream. Couldn't these firms mount a serious challenge to Akamai's hegemony, critics ask?

Of course they could. But I think it is far more likely that Akamai, still the best-known and most-trusted provider, will continue to see big cash flow gains as the youthful market for streaming media and digital downloads expands further. I'm holding the stock in my own portfolio until I see evidence to the contrary.

Find your multibagger
As you embark on your own quest for the next big tech winner, remember the lessons of Akamai. Don't speculate. Seek leaders with obvious and identifiable advantages and the capital to exploit them effectively. Those are the firms that transform thousands into millions.

That's it for our rebellious profiles. I expect there will be many more to write about before long; three more of our winners have doubled in the first two years of the service and appear on their way to still-greater returns. Want to find out what they are? Click here now to get 30 days of free access to the entire portfolio.

Fool contributor Tim Beyers only breaks the rules in his portfolio. Wimp. Tim owns shares of Akamai. Get the skinny on all of the stocks in Tim's portfolio by checking his Fool profile. Microsoft is an Inside Value recommendation. Yahoo! is a Stock Advisor pick. The Motley Fool's disclosure policy is a rebel on Wall Street.