International Scans take 4 hours, and may or may not reveal new information regarding any enemy agent anywhere in the world.
Performing a Local ScanEdit
Each International Scan takes exactly 4 hours to complete, whether it detected any information or not.
The purpose of an International Scan is to acquire information about enemy agents anywhere in the world.
If they yield any information at all, International Scans will usually yield new pieces of existing Clues. This is by far the most common result of such a scan.
Additional possible types of information may be available depending on the current Difficulty setting. On Regional Conflict and below, it is possible to get a piece of an entirely new Clue. On National Threat it's possible to get Solid Evidence about one of the known suspects (I.E. an agent about whom Max already has a Suspect File). On the Local Disturbance difficulty setting, it's possible for an International Scan to add an entirely new Suspect File.
Very often, an International Scan will yield absolutely no information. This is especially true at higher Difficulty settings where information is harder to gather with any method.
Note that Surveillance Quality has no discernable effect on an International Scan. Installing a large number of Wiretaps and Bugs around the city does not increase the chance of acquiring information through such a scan.
Local vs. International ScanEdit
Both these scans take 4 hours to complete, and to the untrained eye may seem to do the same exact thing - but there are indeed differences in how they work.
A Local Scan is more likely to pick up any information (as opposed to none). However, it can only work when the City you are currently in is the residence of at least one enemy agent, and will generally only pick up information related directly to that agent. It is useful when you know someone is hiding somewhere in a City, but don't know where specifically to look.
An International Scan can pick up information from all over the world, and so can reveal Clues regarding agents living in other cities. It does not require there being an enemy agent in the same city where the Scan is initiated. However, it is far less likely to generate any information at all. This method is more useful when you are absolutely stumped about your investigation, and want to find out which city to go to next.