Unsolicited Spam on Home screen

Sitting on the train, my iPhone 5 buzzed with a message informing that I've won 2m pounds (screenshot attached). I'm just wondering how someone was able to spam my iphone and have an unsolicited message appear on my lock screen and I'm particularly worried about what this means for all my other personal information on my phone.

I thought that Apps are vetted. If it is a trojan App then which one is it, and how can fix this security breach?

I should add that my wife has the same phone as I and she got the same message.

My phone has not been jail broken. All the apps have been purchased via the official Apple App Store.

Apologies if this is sounding naive but I've never heard of this happening. Has anyone experienced this or can someone tell me what to do.

For the record, my phone is running version 6.1.4 (10B350). The model number is MD300X/A.

Any help would be appreciated.

Thanks,

Mario

 

Thanks the responses

I have to say it's hardly reassuring. Why is my carrier (Telstra in Australia) allowing Spam to be sent to my phone.

But thanks for the help. If there's any way to stop it please let me know.

Cheers,

Mario