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Since I've realized windows xp's firewall can't block outbound traffic, I need a lightweight solution to block a specific app.
Something along the lines of "little snitch" on OSX would be a great, but I can't find an alternative.
I really wanna avoid running a bloated firewall ala zone alarm for doing just this, so maybe there are lighter weight solutions around...

Know of a lightweight and fast application for this ?

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up vote 2 down vote accepted

That would be as lightweight as it gets (memory footprint of both programs: around 5MB):

Nirsoft's CurrPorts is network monitoring software that displays the list of all currently opened TCP/IP and UDP ports on your local computer. For each port in the list, information about the process that opened the port is also displayed, including the process name, full path of the process, version information of the process (product name, file description, and so on), the time that the process was created, and the user that created it.

In addition, CurrPorts allows you to close unwanted TCP connections, kill the process that opened the ports, and save the TCP/UDP ports information to HTML file , XML file, or to tab-delimited text file.

CurrPorts also automatically mark with pink color suspicious TCP/UDP ports owned by unidentified applications (Applications without version information and icons)

CurrPorts is freeware and portable (no installation required).

If you're looking for a 'real' firewall application for XP, have a look at iSafer (a portable version is available here).

iSafer is free open source freeware.

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Unless I missed something this won't prevent the connection from going through by prompting you. – julien Jan 14 '10 at 23:19
well, you will have to create a rule in iSafer, there's nothing 'automatic' to it, the price of 'lightweight', you know. :) you didn't specify in your question that you want a program prompting you to approve each and every network connection, for this you'll need indeed a fully-fledged "firewall ala zone alarm'. however, iSafer is very easy to setup and use, check the 'English guide'. – Molly7244 Jan 14 '10 at 23:34
Glad you edited your post, as iSafer is just what I needed, thanks. – julien Jan 15 '10 at 0:25
took me a moment, couldn't remember the name ... but you're quite welcome :) – Molly7244 Jan 15 '10 at 0:33

This site recommends Comodo.

I use it on one of my PC's and it seems OK. It's not as good (in my opinion) as the old Sygate Personal Firewall, but that's been subsumed into Symantec's Norton Internet Security which hardly counts as lightweight.

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Thanks, I just grabbed Sygate's old offering, and it's working nicely, using only 12mb of RAM, I'll stick with it unless someone comes up with an even lighter one... – julien Jan 14 '10 at 22:28
@Julien - I didn't know you could still download it. Where did you get it from? – ChrisF Jan 14 '10 at 22:44
Cheers - I thought I'd lost my installer, but when I came to download it I found it. I must get round to replacing Comodo. – ChrisF Jan 14 '10 at 22:56
Comodo used to be a fine software firewall ... up to 2.6.5 or so. then came version 3 and that was the end of it, never touched it since (although i hear it has 'improved'). – Molly7244 Jan 15 '10 at 1:08

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