[arch-general] The principle behind MSN & Yahoo invisible scanners?

[Lukáš Jirkovský]

On 28 August 2010 19:24, Nilesh Govindarajan <lists at itech7.com> wrote:
>  Go to google.com and search for MSN & Yahoo invisible scanners.
> You'll find a big list.
>
> So what's the principle of their working?
> I'm thinking of writing a pidgin plugin to catch invisible buddies.
>

I guess they do some ping-like thing.