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Early Friday morning, a tweet went out from Chicago-based United's account which included an offer for "better sex" and a link to a Web site. The message was quickly deleted and an apology message followed.
The airline has nearly 57,000 followers on the social-networking platform.
Twitter users from around the globe have reported receiving direct messages from their friends saying "This you????" or "LOL this is funny" together with a web link that has been shorted and therefore disguised, which users are directed to click.
When they do, they're directed to a site which appears to be a regular login page. Many will input their login credentials without noticing that the site's address is not twitter.com.
Many applications that hook into the Twitter platform also do not show an address bar, so the user is greeted with an authentic-looking page without being able to verify its authenticity.