Why is there a hosts.equiv file in my /etc folder?
If you are concerned that a file isn't installed by Apple then check the package receipts-

pkgutil --file-info /private/etc/hosts.equiv
volume: /
path: /private/etc/hosts.equiv

pkgid: com.apple.pkg.BSD
pkg-version: 10.6.0.1.1.1249367152
install-time: 1324303327
uid: 0
gid: 0


mode: 644

You can then check the BOM file-

lsbom /private/var/db/receipts/com.apple.pkg.BSD.bom | grep hosts.equiv
./private/etc/hosts.equiv   100644  0/0 0   4294967295


Note the last 0 is the file size and the last field is the check sum of the installed file. Now check the check sum of the file-

cksum /private/etc/hosts.equiv
4294967295 0 /private/etc/hosts.equiv


Note the check sum is the same as what is recorded in the BOM file and cksum reports the file size as zero bytes.