These are harmless memory resident parasitic viruses. They hook INT 21h and writes themselves to the end of COM and EXE files. "Trakia.570" infects the files that are executed.
"Trakia.653" infects EXE files only. Sometimes this virus corrupts the data files.
"Trakia.1070" infects the files that are are accessed. Being executed this virus also searches for EXE files and infects them. It checks the files for specific hexadecimal string and corrects these files, if that string presents at some offsets in the file body.
