To put it as I understand it, using GPL code doesn't automatically make your code GPL; it places a legal requirement on you to either license your code as GPL, or to not distribute the source or product. If the author doesn't license his software, then nobody else can take and use it, but the author is in violation of copyright due to the unlicensed use of GPL code.
The virality of the GPL is a requirement of the license, not an automatic effect upon using GPL code.
