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What: Shares of Criteo (NASDAQ:CRTO), an advertising servicer that helps businesses optimize their Internet-based display content to maximize user engagement, surged by as much as 21% after a newspaper report emerged that Publicis Groupe (OTC:PUBGY) may be in talks to purchase the company.

So what: According to French financial publication Les Echos, Publicis began courting Criteo roughly three months ago, and an agreement to buy the company could be finalized in a matter of days. However, it should be noted, per Bloomberg, that Les Echos did not disclose the source of its information.

If the deal were to be announced, it would hit on two key points that Publicis Group CEO Maurice Levy has stressed since its $35 billion merger with Omnicom Group was called off in May -- namely, a greater focus on digital advertising revenue and making smaller acquisitions. With a current market value of $2.1 billion, and an enterprise value of $1.8 billion (after subtracting cash), Criteo is not too large of a pill to swallow for Publicis Groupe.

Now what: While Criteo investors certainly have to be happy with today's move, we have to remember as investors to focus on the long-term outlook of businesses and not get too wrapped up in rumors, as rumors can just as easily disappear as be proven true.

"What should investors be focused on then?" you ask. Criteo's customer base is a great start. A growing customer base is often a strong indicator of future business health. As of the second quarter, Criteo ended with 6,131 customers, which was a 43% increase over the prior year period.

The transition to mobile is also a key growth driver for all advertisers. Consumers have been moving away from physical computers for years and are instead choosing to surf the web from their smartphone or laptop. Mobile-based ads, and the ability to shape that ad content to optimally target an audience, represents a huge opportunity for the ad industry as a whole. As Criteo noted in the second quarter, it personalized mobile ads for 69% of its clientele.

Finally, Criteo's overseas expansion will be important to monitor. Since the advertising sector is inherently cyclical, advertisers' ability to geographically diversify their revenue stream around the world and in emerging market economies can help offset weakness if it were to arise in more advanced economies. Criteo, in its latest quarterly report, excluding traffic acquisition costs, delivered comparable revenue growth of 67.2%, 61%, and 87.6% in the America's, Europe/Middle East/Africa, and Asia-Pacific region, respectively.