In the second case, the case law is a little less clear. There is no definitive ruling by the Supreme Court and there is some conflict in the circuits. In most -- but not all -- circuits, the whole computer is regarded as one container and plain view again obtains. (You were looking for X under the warrant in the container, and could not help but notice Y.) But it would certainly be better to get a new warrant, just in case.
The DOJ guidelines are here: https://www.justice.gov/sites/default/files/criminal-ccips/legacy/2015/01/14/ssmanual2009.pdf Most of the perinent material in the instant case begins on page 19.
All I am saying is even if contraband is in plain view, the officers will eliminate a lot of time on the stand by getting an amended warrant.
There is no warrant needed for the fed to seize back classified material. It is all belongamick.
Exactly correct. For example a cop legally enters a residence for domestic disturbance and sees illegal drugs in plain view he does not need a warrant to seize the drugs. It was in plain view. As the cops were legally going through Weiner's computer looking for illegal activity (probably child porn or underage girls) the emails were in "plain view." Thus, no warrant needed for the emails. They were in plain view. I suspect that Mr. Weiner is being very cooperative at this time. His ass is on the line for this one!