I have had a message telling me to update my virus definitions.
I have started this, but over half an hour later the program is still spooling, with no apparent progress.
Hello bulworthy, welcome to the community.
Firstly try rebooting your computer.
If it’s not working, then try repairing Avast. Avast user interface => Menu => Settings => General => Troubleshooting => Repair App.
If it still fails, please give detailed information of your machine environment: OS, Avast Product name and versions, other security software including previous one etc.