Data harvesting is when a fraudster contacts you while posing as a reputable organisation in order to obtain and collect your data. Popular organisations that fraudsters like to imitate include: financial institutions, HMRC, TV Licensing, DVLA and telephone or broadband providers.
The contact can seem very convincing. Fraudsters can use logos, make small changes to email addresses and website address/URLs. They can even make a text appear in your genuine conversation chain.
The unexpected contact is a way to try and trick you into disclosing personal and financial information such as your online banking sign on details, date of birth, card numbers and codes generated by your card reader.