The Dow Jones Industrials (^DJI -0.77%) closed out May in record territory, gaining 136 points or about 0.8% for the month. Even though many investors remain convinced that a correction for the Dow is imminent, the bull market managed to defy the skeptics as a relatively strong first-quarter earnings season helped stocks advance. Among the Dow's top performers during the month were Verizon (VZ 0.22%), Cisco Systems (CSCO 0.59%), and Visa (V -0.54%).

Verizon gained almost 7%, with the Dow's telecom giant getting a big vote of confidence from major investors. Warren Buffett was the highest-profile purchaser of Verizon stock, buying about 11 million shares for roughly $500 million, but hedge-fund investors Dan Loeb and John Paulson have also made substantial purchases of Verizon. As Verizon has taken full control of its Verizon Wireless business, the telecom is betting on the success of the U.S. market and its ability to retain supremacy over the industry. With Verizon commanding substantial spectrum assets, it's in great position to build up its lead over its rivals both within and outside the Dow Jones Industrials.

Cisco CEO John Chambers. Source: Cisco Systems.

Cisco picked up 6.5%, with most of its gains coming after a solid earnings report. Even though the networking giant saw revenue decline and expects those declines to continue in its current quarter, investors took heart in the fact that revenue wasn't falling as much as they had feared. With CEO John Chambers finally starting to get optimistic about the company's future, especially its Internet of Things initiative and other forward-looking growth moves, Cisco Systems is in a better position to capture its share of the enterprise networking market. Moreover, if customers start spending more on IT infrastructure improvements, then Cisco should be able to benefit as well.

Visa rose a bit more than 6%, as the credit card network giant breathed a temporary sigh of relief after the situation between Russia and Ukraine became somewhat less tense over the course of the month. For a while, it appeared that because of the economic sanctions that the U.S. imposed against some of Russia's banks, Visa would have to limit its payment-processing activity in the Eurasian nation, and that response led to a dispute that might well have forced Visa and its peers to stop doing business in Russia entirely. However, with a compromise reached between Visa and the Russian government, Visa should still be able to take advantage of the profit opportunities in Russia as it moves toward greater emphasis on electronic payments.