In the fast-paced mobile-apps business, creating a hit app is no guarantee of success: Developers must also fend off the copycats.

App makers say a growing group of 'cloners' are mimicking their products or misappropriating their names and images to ride an original app's success.

The copycats often target top-selling apps and seek to siphon off users and potential revenue. Others carry malicious software. Despite their proliferation, app stores run by Google Inc. and others have been unable to weed them out.

Consider the experience of WhatsApp Inc., a Mountain View, Calif., company that makes a mobile-messaging app that has been downloaded hundreds of millions of times since 2009. After WhatsApp reached the top of the app-store rankings, WhatsApp employees noticed that other apps were hijacking its name to ride its coattails.

Today in Google's app store, alleged WhatsApp clones include 'Whatsapp Nearby,' 'Whatsapp Friends,' and 'Whatsapp Add Me' -- none of which are made by WhatsApp. Those three apps, which were made by the same developer, have been downloaded hundreds of thousands of times. The developer denies they are copycats.

Clones are 'becoming a real problem for us,' said Neeraj Arora, WhatsApp's business chief. 'It does damage to our brand and creates confusion.' It also costs WhatsApp revenue, he said.

WhatsApp is priced at 99 cents on Apple Inc.'s app store, and it is free on Google Android devices for the first year but then costs 99 cents a year after that. Many of the alleged WhatsApp clones are free and generaterevenue by showing ads.

There is little data on how many cloners exist and how much money they are reaping, but the practice can take many forms. Some cloners simply copy the images of a well-known app or use the app's name to cash in on the original app's popularity.

Others employ special software to copy the app in its entirety and swap out its automated advertising provider with one of their own choosing, allowing them to generate ad revenue that would otherwise flow to the legitimate app maker.

Still other perpetrators copy apps and inject them with malicious software that causes a victim's phone to automatically send costly text messages.

App developers said cloning is typically a bigger problem in countries such as China, where the official Google Play app store isn't available. But developers said cloning is also prevalent in top mobile-app stores run by Apple, Google, Microsoft Corp. and Amazon.com Inc. Those four companies declined to provide data on the cloning issue.

Among those app stores, developers said cloning is most widespread in Google Play. Google, unlike the others, doesn't use humans to vet new apps before they are available for download. A Google spokeswoman declined to comment on how common clones are in Google Play.

Still, spokespeople for Google and Microsoft said victims of cloners can file app-takedown requests and that the companies automatically encrypt many new apps to help prevent some forms of cloning. Amazon declined to comment.

Apple, meanwhile, generally connects the alleged victim of a cloned app -- the developer of the original app -- with the alleged perpetrator via email and asks them to sort out the dispute, said developers who have gone through the process. If there is no resolution, Apple will decide whether to pull down the alleged cloned app, developers said.

For developers, a cloned app can take months to remove. David Barnard, a 34-year-old developer from San Marcos, Texas, fended off several alleged copycats in the Apple app store over the past year.

Mr. Barnard's Launch Center app helps iPhone and iPad users create shortcuts so they can perform tasks more quickly. The alleged copycats, called Quick Launch and Voice Launch Pro, surfaced last spring.

Last May, Mr. Barnard emailed a complaint to Apple. Apple encouraged Mr. Barnard to work it out with the apps' creator, Jiqun Zheng. Apple was copied on the emails between Mr. Barnard and Mr. Zheng, who argued that many apps had 'similar features.' The Wall Street Journal reviewed the emails. By late August, Apple informed the parties it would remove Mr. Zheng's two apps from its store, and later removed them. In an email, Mr. Zheng, who separately created a successful app called the Mercury Browser that even Mr. Barnard said he enjoys, said the now-removed apps were inspired by 'some other apps' and had unique features. He said they generated up to $2,000, but it cost more than that to build them.

As for WhatsApp, it is working to remove alleged cloned apps from the Google Play store and said Google's policy-enforcement team has been 'responsive.'

The developer of three of the alleged WhatsApp clones, which generaterevenue with ads, calls himself Freek Martens and said he is from the Netherlands. In an email, he said he makes 'just enough' revenue from ads on the app 'to cover the expenses and finance new projects,' but he declined to be specific.

The developer, who denied the apps are copycats, acknowledged he didn't have the right to use WhatsApp's name and that some people might think his apps were officially associated with the original WhatsApp.

But he argued his apps help WhatsApp because users of his products can make new contacts that then get stored on their phones. If those users later turn on the original WhatsApp app, WhatsApp will be able to scan those users contacts list and allow them to chat with more contacts using WhatsApp, he said.

WhatsApp's Mr. Arora disagrees. 'We don't want more developers using these tactics,' he said. 'It dilutes the experience WhatsApp is looking to provide to its users.'

Amir Efrati

• despite [di´spait]   prep.尽管   (初中英语单词)
• unable [ʌn´eibəl]   a.不能的；无能为力的   (初中英语单词)
• well-known [,wel´nəun]   a.著名的，众所周知的   (初中英语单词)
• advertising [´ædvətaiziŋ]   n.广告a.广告的   (初中英语单词)
• otherwise [´ʌðəwaiz]   ad.另外 conj.否则   (初中英语单词)
• costly [´kɔstli]   a.昂贵的；费用大的   (初中英语单词)
• available [ə´veiləbəl]   a.可用的；有效的   (初中英语单词)
• unlike [,ʌn´laik]   a.不同的 prep.不象...   (初中英语单词)
• comment [´kɔment]   n.&v.评论；评注；注意   (初中英语单词)
• meanwhile [´mi:n´wail]   n.&ad.其间；同时   (初中英语单词)
• victim [´viktim]   n.牺牲者；受害者   (初中英语单词)
• dispute [di´spju:t]   v.&n.争论，辩论；争吵   (初中英语单词)
• resolution [,rezə´lu:ʃən]   n.决心；坚决；果断   (初中英语单词)
• complaint [kəm´pleint]   n.抱怨；叫屈   (初中英语单词)
• journal [´dʒə:nəl]   n.日记；日报；杂志   (初中英语单词)
• mercury [´mə:kjuri]   n.汞；水银柱   (初中英语单词)
• working [´wə:kiŋ]   a.工人的；劳动的   (初中英语单词)
• finance [´fainæns]   n.财政；金融 vt.资助   (初中英语单词)
• guarantee [,gærən´ti:]   n.保证；担保 vt.允诺   (高中英语单词)
• potential [pə´tenʃəl]   n.&a.潜在的；可能的   (高中英语单词)
• revenue [´revinju:]   n.税收；收入   (高中英语单词)
• legitimate [li´dʒitimit]   a.合法的 vt.使合法   (高中英语单词)
• launch [lɔ:ntʃ]   vt.发动 n.发射；汽艇   (高中英语单词)
• unique [ju:´ni:k]   a.唯一的 n.独一无二   (高中英语单词)
• generate [´dʒenəreit]   vt.创造；发生；引起   (英语四级单词)
• automatically [ɔ:tə´mætikli]   ad.自动地；无意识地   (英语四级单词)
• prevalent [´prevələnt]   a.流行的；普遍的   (英语四级单词)
• widespread [´waidspred]   a.广布的；普遍的   (英语四级单词)
• amazon [´æməzən]   n.女战士   (英语四级单词)
• creator [kri:´eitə]   n.创造者；设立者   (英语四级单词)
• separately [´sepəritli]   ad.分离地；孤独地   (英语四级单词)
• officially [ə´fiʃəli]   ad.以职员身份；正式   (英语四级单词)
• malicious [mə´liʃəs]   a.恶意的；预谋的   (英语六级单词)
• inject [in´dʒekt]   vt.注射   (英语六级单词)
• august [ɔ:´gʌst]   a.尊严的；威严的   (英语六级单词)