Visa fraud is the sale, provision, or transfer of otherwise legitimate visas, misrepresentation of reasons for traveling and forgery or alteration of a visa.
Most applicants unfortunately fall victim to such scams, and pay large sums of money to the fraudsters in the hope of receiving their visa/immigration papers.
You can usually detect a scam; When you receive emails with job offers or immigration promises from fabricated email IDs via personal email accounts (Gmail, Yahoo, .co.in, etc.), when advance payments to personal bank accounts are demanded with the threat of visa application rejection or deportation. Beware of visa fraud.