A 30% share price pop used to be a big deal. Champagne corks flying and cigars ablaze, you could celebrate an all-time high and start planning how to sell that stock, now that it was really expensive.

That's not how data security expert VASCO Data Security International (NASDAQ:VDSI) felt this week, though.

Third-quarter earnings of $0.24 per share on $39.7 million in sales represented 60% and 32% year-over-year growth in income and sales, respectively. The stock closed 31% higher the next day. So far, so good.

Shine a different light on the situation, and it's a whole new story. That overnight boost erased three entire weeks of VASCO's share slide, and I can't think of a better poster boy for mispricing than this one. Look up "undervalued" in the dictionary, and it'll say "VASCO." If Rodney Dangerfield were alive, he would joke about getting more respect than this company.

I thought that VASCO was a slam-dunk value play back in February, at $19 per share and a P/E ratio of just 28 -- while easily doubling earnings every year. Well, the stock costs half as much today, at 16 times trailing earnings.

In all fairness, VASCO's customer list is dripping with toxic assets. The company signed up 62 new banks this quarter, and it now counts more than 1,200 financial institutions among its 8,000 users, including some of the largest banks in Scandinavia, Belgium, and the Netherlands. That's the bad news.

The good news is that the governments of the world are helping out VASCO's most troubled customers. Large banks like HSBC (NYSE:HBC) and People's United Financial (NASDAQ:PBCT) can expect a slice of the multibillion-dollar bailout package being bandied about, and both of those major customers have so far weathered the storm better than, say, Bank of America (NYSE:BAC).  

Against that backdrop, VASCO reaffirmed its full-year outlook; its customers might change the timing of a few orders, but they probably wouldn't cancel them altogether. "The overall demand for our products will continue to grow as the number of customers using the Internet to access their accounts grows," said COO Jan Valcke, And you have to go to VASCO or EMC's (NYSE:EMC) RSA Security if you want banking-grade data security these days.

This stock was too cheap at twice the price. Now, it's just getting ridiculous.

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Fool contributor Anders Bylund holds no position in any of the companies discussed here. You can check out Anders' holdings if you like, and The Motley Fool is investors writing for investors.