I believe that just about any computer crime can be prosecuted using existing local crime laws. Computer tresspassing is an equivalent to trespassing. Computer vandalism is equivalent to vandalism. Turning off someone's life support with a computer is equivalent to murder, first degree. Destruction of data is vandalism, the cost of which is the cost of replacing the lost data. Port scanning is walking up to a store and seeing if the sign says "Open" or "Sorry, we're closed". However, lawmakers are not nearly as lenient as I would be. Computer crime laws, at least here in the States, tend to be highly overreactionary and more geared towards punishment than discouragement.
Right now a "get tough on crime" mentality rules the States. One tactic that prosecutors like to use is to press multiple charges against a defendant for a single crime. The way they do this is to call the single crime several different names. Walk down the street and randomly shoot somebody and you'll get aggravated assualt, assualt with a deadly weapon, assualt with intent to cause bodily harm, use of a firearm in commission of a crime, and a bevy of other charges on top of the murder charge. The intent of this is to lock someone up for the longest time possible, longer than a reasonable application of the law provides, and since we've got a lot of crazy people over here the public has no problem with this. It is assumed that because of our high crime rates, jail sentences under the law are not long enough, and new crime laws generally allow for extremely long sentences. Anyone against this line of thinking or proposing preventative measures is assumed to be in favour of more crime, and doesn't get elected.
The text of some of the computer crime laws I've seen seems written in this vein of thought, intended to put computer crooks in jail for the longest time possible. Such things as ten years in prison for defacing a web page, and five years in prison for using encryption in the commission of a crime, are found in the bills being discussed in Congress. I do not think that these are anywhere near reasonable punishments.
Where this international meeting makes things sticky is in Article 6 of the Constitution, a section of which reads: "This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land, and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding". What this means is that international treaties trump the Constitution. If any treaty to come out of one of these meetings calls for mandatory self-incrimination, seizing evidence without a warrant, or shutting down Web sites, there would be no protection under the Constitution for U.S. citizens.