Hi, Niels.

NP>  >  NP> The last job I did was done like that. A BAT file and an EXE
NP>  >  NP> that had at least 20 GOTOs' in it :-) It does a validation of
NP>  >  NP> all the COM EXE etc files on each HD and screams if one has
NP>  >  NP> altered internally.

NP>  >   That's a good idea. I never trust a burglar alarm I haven't made
NP>  > myself, and the same applies to viruses. Some clever bastard can
NP>  > always find a way around the well-known alarms and locks.

NP> Yeah. Inoticed that some had posted a warning about a WORD macro with a
NP> virus in it :-(

I didn't see that, but one bloke at the office got it in his computer
the other day. Maybe. The bloke's a dickhead so could have just been
ignorance.

NP>  >   How do you check the files? It would be easy enough to do your own
NP>  > CRC.... just use a different seed.

NP> How does a CRC work.

A CRC applies a polynomial which is calculated to minimise the
probability of a change to the file ending up with the same CRC.

NP> I just use a checksum of the ascii value of each byte of the file.

Not as effective as a CRC. A simple change like say 2 bytes being
swapped will result in the same checksum for example. There was some
commercial software I used once which must have used that or a similar
approach for the user's registration details. rFakn was as valid a user
as Frank. :-)

I've just coded the 32-bit CRC which PKZIP & ARJ use in (very) fast asm.
It takes 6 minutes to calc the CRC of 5400 files, 220meg, on one of my
hard disks. Also did the 16-bit CRC which all the other archivers use,
and the 16-bit XModem one but didn't bother timing those.

Regards, fIM.

 * * Don't tell me what kind of day to have!!
@EOT:

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