Security firm McAfee is warning people to be on the lookout for fake Android apps that pretend to be one thing but just relentlessly send advertising, the Inquirer reports.

According to the security outfit the apps are designed to look like real ones. There are ones for boosting power, and some pornographic ones. Whatever they purport to be though, they aren't, and McAfee said that they are just shells for shill operations.

Yukihiro Okutomi, a mobile malware researcher at the firm is not keen on the apps and has blogged about them, what they do and why they do it. They do it, he said, in order to serve advertising messages over and over and over again.

"These apps seem to offer no functionality based on their titles, stating 'increase Internet speed' and 'phone hacking,' for example," he said. "Once installed by the victim, the apps appear to work at first but in fact they simply display screens with interactions that are all fake, using hard-coded or random values generated by the code to seem legitimate. In short, these apps are fake or joke applications. These apps also bundle several components that relentlessly show advertisements after the user closes the app."

Users are advised to source their apps from reputable outlets, and we would assume that this means the Google Play store in the case of Android apps.

"As always, users should never install unknown or untrusted software. This is especially true for illegal software, such as cracked applications," added Okutomi. "They are a favorite vector for malware infection."