Practically every modern processor is vulnerable to these new discovered flaws Meltdown and Spectre.
Most certainly, yes.
Probably not. The exploitation does not leave any traces in traditional log files.
While possible in theory, this is unlikely in practice. Unlike usual malware, Meltdown and Spectre are hard to distinguish from regular benign applications. However, your antivirus may detect malware which uses the attacks by comparing binaries after they become known.
If your system is affected, our proof-of-concept exploit can read the memory content of your computer. This may include passwords and sensitive data stored on the system.
We don’t know.