Hi @Fluffo, that 258.8 kB file is an incomplete download, most likely. That's not a complete download file, so I'm guessing the download failed for whatever reason. It might just have randomly happened that the download didn't complete, and some sort of really odd coincidence triggered the anti-virus because the download didn't complete. That's pretty odd, but I'm guessing nothing to worry about.
There's an off chance that a virus infected the file, but I highly doubt it.