I got this in an email message from Skype a couple of days ago.

Problem:
A contraction-forming apostrophe appears where it should not.

Explanation:
The word “it’s” is a contraction of “it is”; the apostrophe signifies the dropping of a letter (the “i” in “is”).

The required word is “its” (not “it’s”) because “its” is the possessive form of “it” (which refers to “Skype”).

Confusing “it’s” and “its” is a common English blunder.

A simple way to remember that “its” is the possessive form of “it” — a third-person pronoun — is to recognize that “his” is the possessive form of “he” — another third-person pronoun — and that neither “his” nor “its” has a possessive apostrophe.

Solution:
“Skype — social networking at its best”