Hmmm...
Is there a lawyer in the house???
The article is basically saying that even though a company bans it's employees from a particular activity, the employer can still be held liable if the employee breaks that ban.
I'm not entirely convinced about this... bit of a sweeping statement...
Vicarious liability is based upon the principle of 'respondeat superior'. Any party which has the right or ability to control the actions of a subordinate can be held liable for those actions.
In the case of the employer-employee situation It's necessary to establish whether or not the act in question occurred while the employee was performing tasks of their employment. In order for this to be the case, the act must have been authorised by the employer.
If an act is not in itself authorised but is sufficiently connected with an act that has been authorised, then it could be considered an 'improper' means of carrying out the individual's responsibilities of employment. Vicarious liability would then apply.... But it gets a wee bit more complex than that
The courts may determine whether an action was a 'detour' and a 'frolic'.
If an employee is acting outside of their normal employment, the employer may still be liable. This will be the case if the employee has taken a 'detour' (that is, if they are still performing the duties of their employment, but simply in a roundabout way). A 'frolic', however, is deemed to have occurred if the employee has acted entirely of their own volition and is not acting on behalf of the company. In these cases, the employer will not be liable.
Now; IF an action is specifically banned it's difficult to see how a vicarious liability can be established...
51) The use of orange safety beacons fitted to motor vehicles is restricted to private land, airports and airfields and while the vehicle is being used for the purpose of inspecting, maintaining, adjusting, renewing or installing video or film apparatus which is in, on, under or over a road, or for any purpose incidental to any such use. One of our T&Cs which the ex-police officers among you will immediately recognise as paraphrased from The Road Vehicles Lighting Regulations 1989. Not only does this paragraph appear in our T&Cs but in our transport policies and procedures document. Why? Well, among other things it effectively protects us from 'causing or permitting' mis-use of these warning lights; such as might happen if an employee parked awkwardly outside the chip-shop on the way home and decided to hit the switch for the lightbar rather than park up properly....
though there's no actual ban on stopping outside the chip shop and switching on the strobes, clearly such an action is outside the limits set by us for the use of the strobes, so switching them on is no longer a 'detour' but a 'frolic'.... And we would not be liable to any extent....
I honestly can't see why the same broad principal would not apply to a company banning the use of IM...
I could cite similar examples in respect of IP law. In fact one of the reasons we're so 'heavy' on the subject of correct, well documented IP management is to protect ourselves and clients from vicarious liability brought about by the mishandling through casual transfer of IP...
Yes you can block port 1863, and that will stop most users, but the savvy ones will use a web client or just connect over port 80. You can end up in a situation where you are spending more time trying to prevent an action than the action itself is losing you.
It changes things when you're talking about potential liability to the business, rather than loss of productivity, or when you have a significant enough user base to justify spending the time.
Presumably though employees would be specifically NOT authorised to circumvent the steps you've taken to prevent the action.. Thus in a 'frolic' situation and relieving you of liability....
if you've got the right IT bods working for you 
