Probably from our Server Status page. However, there are a lot in there which are just "technical" ones, which lost their previously assigned host id or similar.
I remember there was a security program out there which caused arbitrary numbers of such virtual host accounts to be generated, because it was restoring the BOINC directory in a previous state...
BM

Just curious about all those new hosts...
)
This is a weakness of BOINC. Sometimes a host machine has a problem with its BOINC installation and keeps registering itself over and over again. I usually catch this in a day or so and can stop it, if necessary by changing the users authenticator. I periodically delete these 'phantom' hosts from the database.
One of these days David Anderson and I are going to add something where if a user registers more than 200 hosts, for #201 they have to go to a web page and click a button. And then do that again at 400 hosts, 600 hosts, 800 hosts, etc.