If you did not contact the company first, do not give the caller remote access, passwords, verification codes, or payment information.
What legitimate support does differently
A trusted technician should identify the existing service relationship and follow a process you recognize. Microsoft, Apple, Google, and antivirus companies do not cold-call because a random computer supposedly reported a virus.
If remote access was allowed
Disconnect the computer from the internet and call a trusted local IT provider. Do not continue using it for email, banking, or password changes until it has been checked.
This page provides general security guidance, not a guarantee that any individual message is safe. When money, passwords, remote access, or sensitive records are involved, verify through a separate trusted channel.