The One Direction stars - who are joined in the band by Zayn Malik, Louis Tomlinson and Liam Payne - like to do research about what people think about them by creating pseudonyms on the social networking site and asking fans questions who have no idea they are talking to the singers.
A source said: ''Harry and Niall like to get personal with the fans, but it's hard to talk one-on-one with them without being cyber-mobbed.
''So in the last few months they've started using pseudonyms to befriend their fans on twitter. They have no idea the strangers they're talking to are actually their idols.
''The boys change their names every few weeks to prevent being rumbled.''
The teenage hunks - who have 15.4 million twitter followers between them - particularly enjoy doing it while they spend time waiting in airports and airports.
The source added to the Daily Star newspaper: ''They find out what fans enjoy most at the gigs and which songs they like and don't like. It's also a good place to hear what the latest rumours are.
''They say it helps them kill time as well when they're waiting in hotels and airports around the world. Harry does it the most. He loves finding out what the fans really think.''
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