Alien cover up

[Anomalocaris]

If there were extra terrestrials visiting earth today, it would be impossible to cover up. Everyone is walking around with a 5 mp camera in their pocket. There are no aliens, not here.

How do you know aliens won't have effective means of camouflage or disguise?  Or ability to perform observation or manipulation from a distance outside of our effective surveillance?   Or for that matter tap into our systems to render those data we do gathering about them useless?

I think we have no evidence of alien visitation.  Without direct evidence of how many aliens capable of visitation there actually are, how they behave and what capabilities they actually have, we are in no position to assert whether that lack of evidence ought to be expected from well known principles, or if it requires an separate circumstantial explanation.

But we can not preclude the possibility that we are being visited by aliens who are effective to keeping their visit hidden.