I'd recommend updating the anti-virus software. Often game downloaders are flagged (incorrectly) by anti-virus software. I've had it happen too, and then dug around on the 'net to find out what the file is called, and discovered actually it was my a-v at fault not the game downloader.
do a full virus scan (after your update) before you download anything, then try using the downloader again. Personally I am fairly confident about downloads from BFG and certain other sites as they are used by so many people that they have to be extremely careful.
That said, always worth being cautious, so try emailing your A-V provider and seeing if they can verify that it's a genuine virus or whether it's just their software incorrectly flagging a legitimate program.