Type the following as a WordPress comment and see the fun: <a href="https://www.google.com/" rel="nofollow">This is www.yahoo.com link</a>

Imagine Company X provides a service. X is nice enough to offer it for free to education and non-profit sites. However in exchange for the generosity ACME demands that education & non-profit sites place a link on all of their pages to two of X's main products. Would you consider that a link scheme which is in violation of Google's Webmaster guidelines? Think carefully before you answer for you may be surprised.

Most link extractors I know, including the function in WordPress to linkify comments, incorrectly assumes that any text containing https:// is a hyperlink including obvious mistakes like the following: I propose a new protocol starting with phttps://... What do you think?