Inactive Mac: Can a virus in a hard drive infect other files that are in it?

[Peppermint]

So I think my laptop is infected with a virus/malware or something. It slowed down exponentially one time, when no other applications were open. I may be wrong, and if anyone would tell me why it slowed down, that would be great.

Anyway, I have a hard drive and I want to back up everything into it using Time Machine on my Mac. If I have a virus, could it infect the other files I had put into the drive years prior? If so, how could I filter out the virus?

If anyone would like to add any other information that might be helpful, please do!

 

[Broni]

Unfortunately we deal here only with Windows OS so you'll have find some Mac forum.
I'm sorry.