I made the mistake of opening an email attachment in Thunderbird. It was a .xla file, which I opened directly in Excel. The moment that the Excel window popped-up I closed it, realising the mistake I've done.
I ran antivirus checks with Malwarebytes and BitDefender which confirmed the file's malicious. Virustotal.com also flagged the file as malicious. A trojan horse, Agent Tesla type. So I deleted the files and ran more checks, but nothing came up.
I read a bit about .xla files and macros, as I didn't really know how they worked before. Usually all Excel files are opened in "Read-only" or Protected mode, which I believe limits the possibility of running a virus.
Do you think the file infected my PC and I should wipe it clean and reinstall Windows?