An e-mail with one attachment somehow contains 6 files when a friend received it. Also requires few hrs to download.
Double check with sent e-mail. = Pass.
Sent the same e-mail again = Pass.
Scan computer for virus = Pass
Change e-mail password on different PC = Done.
Format HDD = Done.
Many things could go wrong in between, but the first priority is to re-install the main HDD.