Like e-mail, instant messaging has become a part of our lives, at work, at home, at school, on the go -- even on our mobile phones. We take a look at four top chat apps, all of them free, and weigh the relative merits of each.

Multitasking: these days, it's a necessary part of any job and of daily life. So the ability to have a phone conversation while sending several instant messages simultaneously can sometimes make or break a business deal -- or your date for Friday night. Instant messaging is fast, convenient, and -- dare we say -- entertaining, whether you use it at work, at home, at school, on the go, or even on your mobile phone.

We looked at four leading instant messenger (IM) apps: AOL AIM, ICQ, MSN Messenger, and Yahoo Messenger, our Editors' Choice. All are free, although AOL and MSN offer additional features for a price. All are primarily geared toward casual Internet use (AOL AIM offers several business-related features as add-ons) but work acceptably in an office environment as well. In our reviews, we examined these apps' strengths and weaknesses with regard to setup and interface, feature set, and customer service.

Unfortunately, none of these chat apps allows you to talk to friends registered with other services. In other words, your AIM account can't talk to you best friend's Yahoo account -- that is, unless you use another piece of software, such as Trillian. Trillian breaks the chat app monopolies by supporting all four major IMs: AIM, ICQ, MSN, and Yahoo, aggregating your accounts on each into one interface.

If you're concerned about security risks with instant messaging, specifically about buffer-overflow attacks (a common means of penetrating PC defenses) and spim (IM spam), you could try IMsecure, a security product from the people who make the ZoneAlarm firewall. It's the only product of its kind, and it works with AIM, ICQ, MSN, and Yahoo chat apps.

Use our handy chart to compare the features and setup requirements of the Big Four chat apps.

	AOL AIM 5.5	Yahoo Messenger 6.0	MSN Messenger 6.2	ICQ 4.1
Editors' rating	7.6	8.0	7.3	8.0
Registration information	Asks somewhat intrusive questions	Asks less-intrusive questions	Asks extremely intrusive questions	Asks personal information that is optional
What you can customise	Backgrounds	Backgrounds, skins	Backgrounds	Skins, backgrounds, keyboard shortcuts
Business features	Lightbridge Web-based conference calling ($); WebEx Web-based video- conferencing ($)	Video and voice	Video, voice, and whiteboard ($)	Voice and video
Works with mobile phone	Yes, 2-way	Yes, 2-way	Yes, 2-way	Yes, 2-way
Technical support	E-mail (24-hour response), FAQ	FAQs only	Forum, e-mail, FAQ	E-mail (24-hour response), FAQ

Note: $ denotes services that require additional fees.

		AOL AI M 5.5  Despite several business-oriented add-ons, AIM 5.5 is a free and versatile instant messenger that's best suited for AOL home users. That said, we like Yahoo and ICQ even better. Full review

		ICQ 4.1  The free, legendary chat client just keeps getting better; ICQ is the best pick, along with Yahoo Messenger, for features and versatility. Full review

		MSN Messenger 6.2  Relentless offers for premium (fee-based) services turn MSN Messenger into a big advertisement rather than a useful communication tool. For the most free features, use Yahoo or ICQ instead. Full review

		Yahoo Messenger 6.0  The most versatile and best free IM client we reviewed, if you can do without e-mail tech support. Full review

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