Anti Virus

Is there an anti virus for the iphone? I opened an app that I have had on my phone for a few years and use frequently. When I opened it yesterday a message popped up say that something was downloaded but the message was so fast I did not see exactly what was downloaded. As of this point I have not used anything on my phone that requires a password for fear my phone may be compromised.

Yes there is:-

iPhone & iPad Antivirus & Malware Scanner - VirusBarrier iOS 2013

If the phone has not been jail broke then there should be no need since the apps are screened in the App Store in iTunes.