If you ever wonder how to check SHA1 sum on OS X, here is how. Open up a Terminal window. Change the directory to the file location. Issue the following command.
openssl sha1 filename
The openssl can also check the following digests: md2, md5, mdc2, rmd160 and sha. This is useful when you download some files not from the original sites and you want to check the integrity of the files.
I was trying to download the Pwange tool using bit torrent client. After the download was complete, I was surprised to find that the file has been tampered because the checksum is different. I heard that there are increasing interests in the hacker communities about iPhone and Mac OS X. Maybe this is a sign. You might want to check your downloads from now on.