root@ubuntu:~# cd /install/
root@ubuntu:/install# wget skipfish.googlecode.com/files/skipfish-1.05b.tgz
--2010-03-20 12:06:49-- skipfish.googlecode.com/files/skipfish-1.05b.tgz
Resolving skipfish.googlecode.com… 66.102.13.82
Connecting to skipfish.googlecode.com|66.102.13.82|:80… connected.
HTTP request sent, awaiting response… 200 OK
Length: 180023 (176K) [application/x-gzip]
Saving to: `skipfish-1.05b.tgz'

100%[==================================================================================>] 180,023 300K/s in 0.6s

2010-03-20 12:06:50 (300 KB/s) — `skipfish-1.05b.tgz' saved [180023/180023]

root@ubuntu:/install# tar -zxf skipfish-1.05b.tgz
root@ubuntu:/install# cd skipfish/

root@ubuntu:/install/skipfish# uname -a
Linux ubuntu 2.6.28-11-server #42-Ubuntu SMP Fri Apr 17 02:48:10 UTC 2009 i686 GNU/Linux

root@ubuntu:/install/skipfish# make
cc skipfish.c -o skipfish -Wall -funsigned-char -g -ggdb -D_FORTIFY_SOURCE=0 -O3 -Wno-format http_client.c database.c crawler.c analysis.c report.c -lcrypto -lssl -lidn -lz
http_client.c:38:18: error: idna.h: No such file or directory
http_client.c: In function ‘parse_url’:
http_client.c:275: warning: implicit declaration of function ‘idna_to_ascii_8z’
http_client.c:275: error: ‘IDNA_SUCCESS’ undeclared (first use in this function)
http_client.c:275: error: (Each undeclared identifier is reported only once
http_client.c:275: error: for each function it appears in.)
make: *** [skipfish] Error 1

root@ubuntu:/install/skipfish# apt-get install libidn
Reading package lists… Done
Building dependency tree
Reading state information… Done
E: Couldn't find package libidn

root@ubuntu:/install/skipfish# apt-get install libidn11
Reading package lists… Done
Building dependency tree
Reading state information… Done
libidn11 is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 15 not upgraded.
root@ubuntu:/install/skipfish# apt-get install libidn11-dev
Reading package lists… Done
Building dependency tree
Reading state information… Done
The following NEW packages will be installed:
libidn11-dev
0 upgraded, 1 newly installed, 0 to remove and 15 not upgraded.
Need to get 614kB of archives.
After this operation, 1077kB of additional disk space will be used.
Get:1 us.archive.ubuntu.com jaunty/main libidn11-dev 1.10-3 [614kB]
Fetched 614kB in 1s (509kB/s)
Selecting previously deselected package libidn11-dev.
(Reading database… 63065 files and directories currently installed.)
Unpacking libidn11-dev (from .../libidn11-dev_1.10-3_i386.deb)…
Processing triggers for man-db…
Setting up libidn11-dev (1.10-3)…

root@ubuntu:/install/skipfish# make
cc skipfish.c -o skipfish -Wall -funsigned-char -g -ggdb -D_FORTIFY_SOURCE=0 -O3 -Wno-format http_client.c database.c crawler.c analysis.c report.c -lcrypto -lssl -lidn -lz

NOTE: See dictionaries/README-FIRST to pick a dictionary for the tool.

root@ubuntu:/install/skipfish# ls -l
total 864
…
-rwxr-xr-x 1 root root 429335 2010-03-20 12:08 skipfish
…
root@ubuntu:/install/skipfish#

Как вариант — вместо 403 использовать 444. В таком случае nginx просто закроет соединение.
Невежливо, конечно, но зато неплохо экономит трафик :-)