Why does my iPhone download apps by itself is this a virus? If so can you get rid of it ?

If your phone is not jailbroken, you do not have a virus.

Look at Settings>iTunes & App Stores.

Look at the Automatic Downloads section.

It it's turned on, then apps will automatically download to the phone when you purchase them from another device or the iTunes store using yoru Apple ID.

No, it is not a virus! Just a standard feature of the phone called "Automatic Downloads" accessible in Settings > iTunes & App Stores..

Why do so many people automatically assume anything they don't understand or expect is a virus?

As the others have already pointed out, this is probably caused by the Automatic Download feature.

What has not been asked yet is: did you download those apps on another iOS device on the same Apple ID? If not, the most likely explanation is that your Apple ID has been hacked and someone is buying apps on your dime. In this case, you should immediately change your Apple ID password, and should consider turning on the two-factor authentication on your Apple ID. You will then need to contact Apple and see about disputing those charges.