Here is a way to hide text from visitors until they hover over it.
.spoiler {
color: #fff;
border: dotted 1px #f00;
}
.spoiler:hover {
color: #000;
border: dotted 1px #bbb;
}
<p>Who did it? <span class="spoiler">The butler did it.</span></p>
And here's how it works in real life:
Who did it? The butler did it.