I am using whatsapp since 3 years.This is very good app for sending images, videos, pdf files, etc and also very easy to use rather than others, but whatsapp has two negative points.( 1) -Whatsapp have no logout or signout option.( 2) -Donot know who is online, untill you will not open perticular contact name.Opening of contact name is compulsory for knowing user is online or offline.Without open any contact nobody can know, any person is online or offline