some crap virus scanners dont detect actual viruses, they just have lists of filenames, and it happens to be that a certain old virus from the 1990's had a filename called blk00129.dat.
i kinda remember someone posting about this last year
Its not the filename. There actually is part of an old
MS-DOS virus in the blockchain.
Fortunately its harmless.
Like it was mentioned above, you don't actually "execute" the blockchain on your computer so any virus found on the blockchain will not actually be able to do anything to your computer.