Here might be a good place to start. It offers one explanation, at least:
http://linux.die.net/man/8/mailstats The file /var/log/mail/statistics is normally the statistics file for sendmail. The Unix and by extension, Linux philosophy is that data should be textual when possible and binary formats should be avoided, but this isn't always adhered to. The data you have displayed looks like binary data with some blank fields to me. Machine code would be binary by its nature, but the file is not executable, which says that it is not this. Unless you have other evidence of a compromised system, this alone doesn't appear to be a problem. To confirm that it is a statistics file, I would try to read it with the utility mentioned in the link.
My guess is that the PuTTY is a reference to the Putty SSH or telnet client. Looking at the line, it appears that you may be logging in as root remotely. This is not a good practice. Instead, log in via a normal user account and then elevate to root, or better yet use SUDO, for the operations required.
