We had a customer today who had a tech support scam hijack her browser. The scam claimed her computer was infected with viruses which were stealing her banking and credit card information and said she had to call a toll-free number immediately.
This scenario is a typical support scam, and you should never, never, never, call the number.
Happily, she subscribes to our monthly remote support program, and, although terrified, called us first. We removed the hijack and scanned her computer for any signs of malware. After a couple of hours, her computer was good as new, and she had peace of mind.
Your first line of defense is a good antivirus program, and we recommend Bitdefender. Your next line of defense is a combination of Malwarebytes anti-malware premium, anti-exploit, and anti-ransomware.