Hi Leon,
Sorry to hear the experience gave you a bit of scare. If it was ransomware your files on the computer would be encrypted and with an unusual extension, and you will notice you can no longer open them.
I can't answer your question as it's hard to tell what it was without any evidence such as screenshots, logs etc.
However, I can give you some baseline security advice to help you minimise the likelihood of of a similar scares in the future.
- Ensure the account you use on your operating system (OS) is not administrator. Many OS-es allow you to create limited/standard user accounts. Admin account should only be used to make changes to the OS when needed.
- Use a modern web brwoser such as Firefox, Chrome, Safari or Edge.
- Regularly ensure both the OS and browser are up to date.
- Use an ad blocking extension for your browser. Example: uBlock Origin, pretty happy with it.
- Disable browser notifications. Example for Chrome: https://www.avast.com/c-turn-off-chrome-notifications
- This one is a bit more technical, so be careful before going ahead and note down previous setting. Change the DNS settings assigned to your computer on either the internet router (look for the DHCP option) or on your computer network interface (wired or wireless depending on your setup). The easiest is probably to set it to 1.1.1.1 which is Cloudflare owned and have protection against malware. Again, make sure you are comfortable before making any change. If unsure, get someone with network knowledge to set it up for you.
In addition to above, the Australian Cyber Security Centre has plenty of guidelines how to protect yourself and your family when online, recommend reading through:
https://www.cyber.gov.au/protect-yourself