A program released by Mirablis that allows person to person communications without needing to know exactly when the other will be online. It communicates thru an ICQ Server that allows instant notification of users being online, and storing of messages, files, etc, for later delivery when they are.. Mirablis has been bought by AOL, who most people think will become the demise, as AOL has a competing, but inferior product called Instant Messanger..

Actually, ICQ uses a direct connection between users to send messages, unless you go to the Preferences dialog and specifically tell it that it should send messages through the server. And, even then, files will still be sent directly. AFAIK, you can not store files on an ICQ server.

Since nobody else could be bothered to list them, here are a few of ICQ's features:

• Instant Messages (of course)
• Shows when other users on your contact list are online (assuming they are not in invisible mode)
• Invisible mode, so others can not see that you are online
• Invisible list, so you can specify specific people who can not see when you are online
• Ignore list
• URLs (so you lazy people can just click a button rather than copying a URL to the clipboard and pasting it into your web browser)
• External application support (so you could, for example, start Netmeeting with another user right from ICQ with just a couple clicks)
• File sending
• User groups (so you can make a group for your friends, a group for your enemies, a group for artichokes, &c)
• External plugin support
• Comes with voice-chat plugin
• Real-time text-chat (by that, I mean you see what a person is typing as (s)he types it) or, if you prefer, IRC-style chat. Supports as many users at once as you have bandwidth for.
• Custimizable sound events
• With ICQ Plus, you can skin it

Here's my knowledge add for this issue:

Here is a small list that might be usefull to realize. I discovered it when setting up an IF-MS (Information Flow Management System) policy.

• digital archiving (cheap, permanent, steadily growing, low usage, high in meta data)
• permanent physical archiving --> stuff required by law (very expensive)
• temporary physical archiving --> for: high usage reference data (very cheap, fast access, high usage, no/low meta data)
• delayed digital interaction (very cheap)
• delayed IRL interaction (cheap)
• instant full contact digital face 2 face, like: Instant Messaging or video conferencing (expensive, little meta data)
• instant low contact digital face 2 face, like: Instant Messaging (cheap/expensive, no meta data)
• instant IRL mono/multi face 2 mono/multi face (expensive, very temporary, inefficient in knowledge management, efficient in knowledge creation, moderate/efficient meta data)
• instant mono face 2 multi face (cheap, more permanent, moderately efficient in KM, inefficient in knowledge creation, efficient meta data)

PS: The new releases since ICQ 2001 stores the UIN's on the Mirabilis servers ! Make sure you backup and trust Mirabilis when using this IM software.

It may seem weird that ICQ is how we communicate in my company, but before you judge, take a look at my reasoning:

• I use LICQ, a lightweight ICQ clone for Linux; all good.
• LICQ 0.85 supports encrypted peer-to-peer messaging
• everyone in the office is given nice Sony headphones when they start; as a result everyone listens to music when they work, making it hard to talk directly
• since talking wastes valuable programming cycles of my brain, ICQ is a God-send; it forces people to choose their words carefully as it takes them much longer to type their message than to speak to me

I have had ICQ for several years, since close to the beginning. I know from conversations with various people that originally the numbers were assigned somewhat randomly and the fact that you had a 7-digit UIN does not necessarily render you "l33t". I originally was #5701550, but since the servers were notoriously bad at the time, they never saved any of my information so that when I finally forgot my password they refused to email it to me on the grounds that they did not have my email address on file. I was a tad miffed. Currently, that number has no info at all, although it once had my Nick of the moment.

I use ICQ to communicate with people from around the world, including people I originally met through Hardwood Hearts, Hardwood Spades, The SciFiVine (originally SciFiSites), imood, here, and various other places around the internet. I also use ICQ for the purpose of exchanging pictures, exchanging mp3s, and voice messaging. It has come a long way from the program I originally downloaded so long ago and the latest release sports a revamped User's Details window and a few fixes.

One thing particularly notable in the latest version is that the plugin options have been separated from the main program. Now, when you download ICQ, you get only the basic program. If you wish to have ICQ Voice Message, ICQ Help, or ICQ Web Front, to name a few, you will have to visit the ICQ Plug-in Center at the Mirabilis site to download those. The ICQ download is currently 5.1mb.

Unfortunately, there are some odd compatibility issues when converting the user database from ICQ99 to ICQ2000 and if you are particularly unfortunate, you may lose your entire db. This happens rarely, but when upgrading you should always backup your db in case of this so that you don't have to lose everything, although what you would do with it outside of ICQ I couldn't tell you. My db had been corrupted and I was completely unable to convert it. The loss actually freed about 148mb of space on my hard drive that had been taken up with the message history of several years.

My current UIN is 22746352, and at this moment my Nick is Neko no Aijo.

As great and useful (and secure as a wet paper bag) as the technology is, there are some minor problems with the client software.

Clearly, Mirabilis's developers (or chimps, as I like to call them) are the biggest collection of Visual Basic-reared jackasses ever to draw breath. Their client software is crammed with useless features*, and has an incredibly ugly and unintuitive interface.

An interface that, for example, doesn't use the right-click for anything apart from a message telling you to use the other button. That prints user details in grey on a grey background (and doesn't let you highlight them, or change the colours). That resizes and repositions itself stupidly whenever an OpenGL or Direct3D application does a resolution switch. That features banner ads in places where other clients don't have places. And features a barrage of crappy sounds that have to be turned off or erased to maintain your sanity.

And don't get me started on the options dialog ("look how many controls we can fit on a form!"). Why don't AOL sack these buffoons and let those fine fellows at Nullsoft (whose souls... err, company they also own) do their l33t interface-fu on it?

Thankfully, there are many alternatives available to the ICQ junkie, such as the slinky MICQ, or the highly competent Trillian.

*the SMS function is pretty cool though.

ICQ protocol wasn't published at first, but people reverse-engineered the protocol when the only client that was available for Linux was That Big, Slow, Ugly And Buggy Java Client®.

When reverse-engineered (first by Magnus Ihse), the v2 protocol turned out to be quite horrible. Apparently, the latter versions of protocol, as well, sucked similiarly but differently.

For long time, the passwords were sent unencrypted. The connections were almost always over UDP, making it (without any precautions in place against it) spoofable, hijackable, and not guaranteed to be reliable - and also difficult to deal with in places with firewalls. Also, the client developers noted the official clients were crashy when fed some bad packets...

The clients had "hooey permission bits" - you can set the permission bits all right, but the client is not required to honor them. One of these permission bits is "require authorization in order to add me to your contact list". Well, I edited my mICQ contact list and the "unaddable" users got to my contact list all right... and the users didn't even get a confirmation message that I had added them! Same thing with Everybuddy, I'm not sure if Jabber also did that...

The newer ICQ protocols have fixed the UDP problems effectively by getting rid of it and using a new, hopefully better protocol.

And since the aquisition by AOL, the new winds blow: Newest versions have apparently switched to use AIM OSCAR protocol. (thanks, fuzzie.)

(Oh: My UIN is 4291042 - I hadn't even read Douglas Adams' books yet when I first used ICQ... Though, these days I use only Jabber: wwwwolf@jabber.com.)

The latest version of ICQ - 2001b (released November 4th 2001) contains a feature which enables users to share directories on their hard-drives with users on their contact list.

This feature is quite similar to the sharing capabilities of peer to peer networks and applications such as Napster, Gnutella, KaZaA, Audiogalaxy, etc.

The only difference between these networks and the ICQ implementation is the abilty to search for the files you wish to download. It is likely that future versions of ICQ will contain this feature, and will make ICQ join the mp3 and divX piracy world, also making Mirabilis a target to legal attacks from the RIAA and similarly oriented organizations.

But even before such a search service is implemented, the broad use of ICQ may make the directory sharing feature a replacement for current 'illegal' file distribution methods such as IRC xdcc bots and fserves, FTP sites, etc.

ICQ as a name dates from Ham radio days, being an abbreviation for I Seek You. This was, and still is, used by radio operators when tentatively looking for a specific radio operator, e.g.

"Juliet Bravo this is Sierra Seven. ICQ, Over."

Although the official ICQ client is a clunky piece of bloatware with some reported problems with system stability, there are alternative programs which use the ICQ protocol, of which the following is a non-exhaustive selection, available from an internet near you:

• A stripped-down interface (currently only using Mirabilis's server) is available on Windows versions of the Opera browser, from version 5 onwards. The whole browser package is smaller than the official ICQ client. I have found this to be quite adequate for limited use, but I use Opera anyway.
• Miranda is an open source stripped-down Windows and AlphaNT client designed for mouseless operation.
• mICQ is a command-line console interface vaguely modelled on mIRC for Linux, BSD, Amiga, Win32, BeOS and "some other *ixes".
• Trillian is a skinnable freeware Windows client that also covers several other messaging protocols (AIM, IRC, etc.)
• Linux (X) users can use licq or gicq.
• It is left as an exercise for the reader to work out what OS AtarICQ runs under.
• A web-based Java client can be reached at http://go.icq.com - predictably, it is only really happy running on the Microsoft Java VM but OK at a pinch otherwise; handy if you only have access to port 80 or are on a machine where you don't want to or can't install anything.

Mirabilis fights all other icq-cmpatible implementations of clients and servers with gateways.
Still, you could get a free ICQ server - IServerd and free gate to Jabber - icqtransport.

ICQ is not a secure protocol. There was a client (I do not know it's name, it was written by someone from Ukraine) which have had ability to send messages from any UIN number you like. Also you could intercept messages for other persons and get passwords with it. Instead of securing icq's protocol, Mirabilis insist on removing the WWW page with this software and calls it illegal.

There is Perl implementation of ICQ client for Unix console - vICQ.

Surprisingly, perhaps, this has not happened. I've been on ICQ for yonks now: I first joined the network when I was 9 or so and had an 8 digit UIN (and went by the name of Joebee B, the shame). I remember seeing it in action on my dad's first PC, and hearing and being terribly amused by the distinctive and extremely irritating "eh oh!" sound that heralds new messages. The quality of service has, I've noticed, gone up noticeably since then. AIM and ICQ users can now communicate with each other, which has led to ICQ having an even bigger reach among internet users. The client software has plenty of capability, and no longer looks as pig ugly as it did before (Windows XP users suffered for ages with this, as ICQ did not accept the XP theming abilities and defaulted back to a nasty variant of the Windows Classic theme). It can be used as an email client, a video chat program, a white pages and, of course, a top notch IM client. All in 4MB.

Certainly, ICQ seems to be the better IM network out of the big three (MSN, AIM, ICQ). ICQ doesn't seem to have so many of the script kiddie wannabees as AIM, and certainly less of the tweens that so plague MSN. Most of the people on ICQ are clued in, know their shit and are intelligent. That's not to say that there aren't intelligent people on MSN or AIM, just far less of them.

In any case, ICQs network is the only one which is truly international. A search through Random Chat is always revealing: you could be talking to someone in Slovakia, then someone from Bulgaria within a few minutes. I've met Americans, Austrians, Japanese people and Brits on ICQ, and if you want to chat to a large percentage of people around the world ICQ is the way to do it.

That's not to say ICQs perfect. The ad banners at the bottom of the windows are irritating, but easily ignored, and this is merely a blemish on a nice package. Sadly, people seem to be using MSN more after Microsoft's inclusion of MSN Messenger with Windows XP, and to that end ICQs days may be numbered after all. Still it's one of the better IM networks out there and one that should be tried by all at some point in their internet-using lives.