The race to gain new users has seen a number of apps using “an aggressive form of ‘growth hacking’ that makes it difficult for users to opt-out of sending invitations to their contact lists”, according to mobile security specialist AdaptiveMobile.

Growth hacking is a method of increasing the user base of an app, for example by sending invitations to contacts via SMS. The company said it started tracking the trend and its associated ‘App Spam’ earlier this year, noting that Google recently updated its Play terms to state that titles must not be involved in unsolicited promotions via SMS.

Five social, gaming or messaging apps were identified as the most aggressive in sending out SMS messages to a user’s contact list, while also making it difficult for users to opt out. These are: Glide, Meow, Tango, Skout and Pixer.

After monitoring invitations sent during the period, AdaptiveMobile said that Glide sent 57 per cent and Tango sent 19.7 per cent. This meant that Glide sent out more than 10 times more SMS invites than market leader WhatsApp.

Although Tango allows users to opt-out of installing contacts when installing an app, it also includes an “invite on activity” feature, so that when a photo is taken using it, more invitations are issued.

“It’s common to invite friends to new apps, but this shouldn’t turn into spam. These apps take this principle above and beyond acceptable limits, subverting communications between friends and contacts,” Cathal McDaid, head of data intelligence and analytics at AdaptiveMobile, said.

The company has drawn up a set of recommendations for developers to ensure that apps do not lead to complaints from users. This includes not giving an ‘invite all’ option, not pre-selecting all contacts on invitation screens, and not including invites as part of an incentive system (to win points, for example).

“If an app choses to send invites, and if this is permitted by the relevant app store and mobile operator, then it needs to make sure that safeguards are built into the design to ensure that a user can easily opt-out,” McDaid said.