As smartphones and the applications that run on them take off, businesses and consumers are beginning to confront a budding dark side of the wireless Web.

Online stores run by Apple Inc., Google Inc. and others now offer more than 250,000 applications such as games and financial tools. The apps have been a key selling point for devices like Apple's iPhone. But concerns are growing among security researchers and government officials that efforts to keep out malicious software aren't keeping up with the apps craze.

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