CRC?

안녕하세요
전에 보호기를 만들기로 결심했던 1人이에요!

전에 올린 글 댓글에 crc를 사용해보라는 수다님의 댓글을 보고
crc가 뭔지 검색했는데
수다님께서 만드신 hall보호기(맞나?) 가 있더라고요
안을 들여다 봤는데..

private sub form_load()
dim ccrc32 as new ccrc32
dim lcrc32 as long
dim cstream as new cbinaryfilestream
dim crcs as string
if getsetting(slow, slow dll protector, hal-crc) = vbnullstring then
msgbox hal.dll 의 crc 값이 저장되어 있지 않습니다. & vbnewline & _
확인을 누르시면 저장합니다., vbinformation, 알림
cstream.file = environ$(windir) & \system32\hal.dll
lcrc32 = ccrc32.getfilecrc32(cstream)
crcs = hex(lcrc32)
savesetting slow, slow dll protector, hal-crc, crcs
if len(dir(environ$(systemdrive) & \temp_f1.slw)) = 0 then
if len(dir(environ$(windir) & \system32\hal.dll)) = 0 then end
filecopy environ$(windir) & \system32\hal.dll, environ$(systemdrive) & \temp_f1.slw
shell attrib +a +h +r +s & environ$(systemdrive) & \temp_f1.slw
end if
end if
end sub
private sub tmrhalcheck_timer()
dim ccrc32 as new ccrc32
dim lcrc32 as long
dim cstream as new cbinaryfilestream
dim crcs as string
doevents
sleep 10 .

if len(dir(environ$(windir) & \system32\hal.dll)) = 0 then
filecopy environ$(systemdrive) & \temp_f1.slw, environ$(windir) & \system32\hal.dll
shell attrib -a -h -r -s & environ$(windir) & \system32\hal.dll
exit sub
end if

cstream.file = environ$(windir) & \system32\hal.dll
lcrc32 = ccrc32.getfilecrc32(cstream)
crcs = hex(lcrc32)

if getsetting(slow, slow dll protector, hal-crc) crcs then

filecopy environ$(systemdrive) & \temp_f1.slw, environ$(windir) & \system32\hal.dll
shell attrib -a -h -r -s & environ$(windir) & \system32\hal.dll
end if
end sub

제가 머리가 안좋아서 이해가 잘 안가네요 어떤원리인지.. ㅋ
자세히 좀 설명해주실분 구해요!