There is another system that only detects hosts up or down with a timeout system. This system try to load an image from a given host and port but if it is not possible in a given time it shows a message, but I think this is worse and with a lot of false positives. It works in Firefox and IE, but I think only is useful to detect hosts up but not ports open or closed. More info in Gnucitizen
Scan hosts: scans a range of numeric dotted ip addresses ( like 192.168.2.100 ) on the same port port and shows the responses of the hosts.
Scan ports: scans a range of ports on the same host and show the responses in the same way than scan hosts.
Ping host: launch only one request on the given port and host and response.
Fixed timing: launch one request each x seconds
Random timing: all requests are launched randomly into a time window of x seconds
Sorted scan: if checked the pending requests are launched in order, otherwise randomized
C o m m e n t s : h i p e r n e s @ u s e r s . s o u r c e f o r g e . o r g