It looks it found something infected. What should I do about this?
I am only an F-Secure user (their home solutions). So, only unofficial suggestion.
You could to proceed with "Quarantine" option. Items (multiple) will be quarantined if possible.
Note that since detection is about 'system-wide' trouble, but detection name is about "Potentially Unwanted" (https://www.f-secure.com/v-descs/guides/classification_guide_pua.shtml) and "!Online"-mark - there can be false positive detection based on too generic triggers.
Actually, this detection can be about multiple suspicious items over the system (with one type of detection name) or something like browser's extensions or addon (toolbar).
OR one executable or malicious-rated file under critical system folders.
However, it can be also from "Downloads" folder.
When you tried to use "Quarantine" option - then found items should be quarantined (or removed) and small clean up is performed.
If you would like to understand what is actual file/items there - maybe you can try to contact F-Secure Official Support Channels (for example, chat) for remote assistance and proper help:
Sent the guarantined files to the F-secure inspection by using the ftp.