The basic answer: Tracking individuals on the internet is a very difficult and time consuming task. If someone wants to stay anonymous on the internet they usually can. The reason why: Basically there are very few things to trace individuals down with. The most common of which are IP addresses, which uniquely define a single connection to the internet at a given time. Responsable Internet Service Providers maintain logs connecting users and their corresponding IP address for the periods of time they are logged on, however the US governement requires search warrents in order to obtain this information (user privacy is important to everybody. The US governement needs a warrent to search your house, they need a warrent to search your computer). Beyond these legalities within the US, the US governement has very little, if any, control over foriegn ISP's and may not be able to gather this information at all. On top of all of this computer savy internet users can easily hide all of their information behind proxy computers. Proxy computers are computers that sit on the internet, allow incomming connections and forward them to their destination, but reveal no information about the source computer. Fortunately not very many open proxies (anyone can use them) exist. Unfortunately hundreds of thousands of computers on the internet have become unwitting accomplices to these illegal activties through the use of viri and trojan horse programs designed to turn the everyday computer into an open proxy. For a terrorist to become untrackable they only need to find one of these infected computers and conduct their illict buisness through this computer. Typically there is no way to trace the invidual beyond this infected computer.

There are electronic tracking or spy stations in the U.S, England, New Zealand, and Japan which are referred to as "Echelon" They basically record every communication sent by email, computer or cell phone, but the volume of data is enormous and sorting through it all is almost impossible. They do have certain words and phrases "flagged" which means if you use a word like "bomb" in your email for example, your message gets flagged automatically and put into a different category for more urgent attention, but even that category has too much info to handle. Terrorist plots have been thwarted by use of info picked up at these stations but it's more likely because they had some tips on where to look beforehand. Also, lately Bin Laden has quit using electronic communications and gone for the low tech word of mouth approach.

They are when possible.

They probably don't rely on either.Person to person is a safer way to communicate.