I have not heard of a contaminated ‘zipping’ program that added a virus during compression. I have had repeated occasions where a ‘filtering’ service declared all ‘zips’ to be viruses, default settings of block .exe .vbs .zip are not uncommon because they are easy. To actually investigate the content of a ‘zip’ file is not easy especially is it is encrypted for security. (You did not say why the text files were zipped in the first place.)
Are you receiving ‘sip’ files from anybody else?