Today a number of websites are providing free WordPress plugins and themes. But the main issue is that you can not trust sources other than official WordPress repository. Most of the people who provide free themes use malicious code to create them which is really hard to find. And, they do so with the intention to hack those WordPress websites in which such themes are installed.
secure.wphackedhelp.com/blog/detect-malicious-code-malware-wordpress-themes-plugins/
