Virus Trojan Malware differences

With smartphones growing also increases their vulnerability; not only because smartphones are small and easily to lose, but also because they present a big target for same kinds of security threats that plague PCs -- viruses and other malware.

Differences between Virus,Trojan and Malware

Viruses are theoretically possible for any OS, Trojans are another matter. Viruses are a class of that self-replicate.
A virus is malware that grows and self-replicates.
Acomputer virus can weaken a system so secondary infections are possible. 
A Trojan is malware that claims to be one thing, but it's goal  is to secretly sneak in with your apparent permission and  compromise your data.

A worm can be part of a Trojan or part of a virus.It fails your machine by break down operations.
Spyware is malware targeted to compromise your data. It can be part of the payload for a virus or a Trojan.