SAN FRANCISCO (AFP) - WhatsApp recently patched a flaw that left 200 million users vulnerable to being hacked using booby-trapped digital cards for contact details, according to a US computer security firm.

Facebook-owned messaging application WhatsApp boasts more than 900 million users, some 200 million of them who access the service on computer browser software that mirrors activity from mobile devices.

A flaw in the web version of WhatsApp made it possible for hackers to hide malicious code in seemingly innocent "vCards" containing contact information.

Opening tainted cards allowed viruses to infect computers, potentially allowing hackers to steal control or information, according to an online post by Check Point computer security firm.

Hackers would only need a target's smartphone number and for the person to open the "vCard."

Check Point said that it disclosed the vulnerability to WhatsApp last month and that an updated version of the application was released.