Use the adjective unscrupulous to describe someone who behaves in a dishonest or unethical way.
Unscrupulous behavior is the unfortunate resort of many ambitious people — it’s the immoral stuff they do to make success more attainable. When you sell someone bad loans, when you hack into your competition's accounts, when you read your roommate's mail for signs of an opportunity with his girlfriend, you're being unscrupulous.
