Why public IMs are not good for business use?

Public IMs are not appropriate for business use for many reasons. The first one is Security, which includes a variety of issues:

Confidentiality: Public IM communication protocols are not encrypted. This might not seem like a big deal since other unencrypted communication protocols, such as email, are still used for business. But there is a difference: if your company has its own email server, those emails you send from your office to your boss' next door never leave the corporate firewall. Even if your ISP hosts your email, what you send just travels one link towards your ISP. On Public IM networks, your messages travel unencrypted all the way to the Public IM server .
User Authentication: Public IMs make it very easy to fake an identity. All you need to do is register an account and set the name and/or email address of the identity you would like to have under your own profile information. This can and is used for fraud or to obtain confidential company information from employees who, for example, believe they are providing that information to a coworker. You may think that this problem is similar in email, where faking an identity is also easy, but there is a huge difference. If an employee replies to an email from a fake identity, the owner of the email address, and not the person faking it, will be the one receiving the reply. On public IMs the reply will go directly to the person faking the identity. This person is also practically impossible to track down and identify.
Privacy: Even though all public IMs offer some type of privacy settings and allow you to specify if your authorization is required when someone wants to add you to his contact list (and monitor your availability status), in some of the Public IMs that feature is poorly designed and can be easily worked around. The result is that anyone could be watching your presence availability status without you knowing about it.

But security is just one of the problems of using Public IMs for business. Other issues include:

Deployment & Management: If you are planning to deploy a Public IM in a medium-sized or large organization, how do you create the user accounts? It is not possible to integrate with your existing user directory so you will have to ask each user to fill out a form in order to create his account or an administrator would need to spend days creating the accounts for everyone. Also, what username will each person be known as in the public IM network? Ideally, it should match their current username within your network, but with millions of users on the public IM networks, your first choice will probably be already taken. You will end up with usernames like jsmith3476 which leads us to a related issue which is how users find each other. On most public IM networks it is difficult to find a specific user unless you have his username or ID. How much time will your employees need to waste passing each other their usernames on the public IM network in order to setup their contact lists?
Control: Do you know which of your employees are using IM and what they are using it for? When using a public IM, all of your employees can communicate with any user on that public IM network. Do all your employees need to communicate with users outside your organization? If your company has a policy regarding the usage of IM for non business purposes, how can you enforce it? With public IMs there is no way to do so. Plus, if a communication misunderstanding arises, there is no trusted centralized message archive you can look at to verify who said what.

A private IM network based on Instan-t not only solves all these issues; it also offers collaborative features not available in public IMs and allows a high degree of customization and integration to meet your specific needs.