A hoax advert shared on social networking sites has tricked iPhone users into thinking the latest software upgrade had also made their phones waterproof.

The hoax claimed that iOS 7 included a "smart-switch" that automatically protected the iPhone's "delicate circuitry ... it will shut off the phone's power supply and corresponding components to prevent any damage".

The misleading rumour was circulated on Twitter, Facebook and other social networking sites and reinforced by a convincing spoof advert which mimicked Apple's own marketing material.

The prank is believed to have originated from the controversial internet forum 4Chan.

Fooled by the fake advert, which included the statement "waterproofing covered by Apple's warranty policy", some users reportedly upgraded their iPhones with iOS 7 and dunked them in water to test the new feature – only to discover they had just destroyed their expensive smartphones.

Apple's new iPhones, including the iPhone 5C and 5S, cost between £469 and £709 without a contract, depending on the model. At launch in September 2012 the iPhone 5, last year's Apple flagship phone which also works with the new iOS7 software, cost £529 direct from Apple.

Several users took to Twitter to vent their frustrations, including Joe who said "Ok whoever said iOS 7 is waterproof GO F*** YOURSELF, " and Ricardo Tamayo who also seemingly fell for the prank too: "Whoever said iOS 7 is Waterproof your phone.... F*** You".

The iOS 7 update – which does not make devices waterproof – was released on 18 September, and despite suffering from frustrating download delays, saw enormous demand that doubled both UK and German internet traffic and is estimated to have been downlaoded 100m times within 12 hours of release.

• iOS 7 is a complete visual redesign of Apple's iPhone, iPad and iPod touch operating system combining flat design with bright colour and enhanced features.