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What's happening? 
In an extension of last week's drop, shares of Yandex NV (YNDX) plunged as much as 10% early Monday as the Russian ruble fell to new lows against the U.S. dollar.

Why it's happening 
As of this writing, the dollar trades for a record-high 65.79 Russian rubles -- compared to around 58 rubles per dollar on Friday -- amid falling oil prices, sanctions, flight of capital out of Russia, and, consequently, worries that some of the country's largest businesses could potentially default on their dollar-denominated debts.

To be sure, though Yandex performed admirably in its most recent quarter, it does generate the vast majority of its revenue in rubles as Russia's dominant search engine. What's more, any subsequent economic weakness stemming from Russia's struggling currency could have negative repercussions for Yandex's core advertising business. And while its unique leadership position could very well help Yandex survive and thrive going forward, as long as Russia's general strife persists, so, too, will the volatility in shares of the companies operating within its borders.