Do I have a rogue sticky note and how do I make it vanish?

Out of the blue a small window appeared with a line of text which was relevant to what I had been doing but was not asked for by me. A bit of research suggested it might be a Sticky Note from KDE desktop but had no editing features or means of closing it. I tried to clear it and that wiped the line of text but still it sits there. This note has the colour of my console window, not the dirty yellow from KDE Knotes and I have never used or wanted this feature.
How can I get rid of it?

Unlock widgets, click it, or hover over it’s top, and you should see the controls of the widget. Don’t forget to lock the widgets afterwards.

If widgets are unlocked, and you paste some text to the desktop, you will get a sticky note.

It is very easy to accidentally paste text to the desktop. Just an accidental middle click (click on scroll wheel) can do it.

I keep widgets locked to avoid this.

And yes, it can be removed, as described by Knurpht.