The last few days I noticed strange stuff in my access log:

Code:
188.107.245.66 - - [18/Oct/2011:19:12:19 +0300] "S\xe5\v\xa1\xdcJ3\b\x86V\x06\xdf\xfc\xe12\x17\xcf5\xcc\xe4\xceF" 400 226
188.87.22.67 - - [18/Oct/2011:19:45:57 +0300] "\x86E\x80\x1aAv_t\xef\xc1\x15\xe6\xf6G\x136\xf6\xb2\x10d\xd0\xd4\x8d\xb8\xbe!\xd0\xe1f" 302 -
81.157.125.118 - - [18/Oct/2011:20:22:03 +0300] "\xd9V\xdd\xfa[l_\"l\x8b=\xa9\x02\x87\x81\xccV\x843\x0e\x18\xbb\xd9X\xb7\xcf\xc5\xaf\xf6P\xff\x81\x92\x0e\x9bld\x7f\x83<YA\xd2\x0c\x8e\xfd\xcb\xab\x85\xc6" 400 226
82.113.121.32 - - [19/Oct/2011:19:56:34 +0300] "\xfd\xe8\x1clL\x04\x12\xeau\xf6v>\xc4\xd8\x8b\xea\xf1\xd2<\x11\xe9\xfa\xa1\x89\xd7\xc3`\xb0\xc5(\x07\xde\x12\x88\xb8\x9b\xfc\xf7kq," 302 -
77.181.227.10 - - [20/Oct/2011:19:01:44 +0300] "\x9a\xaf\x1b" 302 - "-" "-"
194.228.94.242 - - [21/Oct/2011:12:31:49 +0300] "$\xfe\x87O\xa7\xb6\x0e\x17[}" 302 - "-" "-"
188.187.133.114 - - [21/Oct/2011:20:19:35 +0300] "M\x85r?\xf3\x81\x13\x0e\xc8\xab" 302 - "-" "-"
95.103.75.20 - - [22/Oct/2011:16:41:58 +0300] "\xc0\xfd\xbf\xcf" 200 194 "-" "-"
46.135.104.255 - - [22/Oct/2011:16:58:52 +0300] "w\xc1\x15\xadqk\x85\xa18\x83\xf0\xe8{\x95\x10\x92}\xa8\x9e\xddt\xcdiA\x02\x17G\xf1R\x96p" 200 194 "-" "-"
93.96.74.252 - - [22/Oct/2011:23:25:37 +0300] "\xfbO\xed\xda\x85$\xa8\xa6\x8e\xcdi\xc6\x13't$\xc1 1\xa8\xec4(\x98\xc3\xda\xbc\x8b," 400 226 "-" "-"
Normally I see this:
Code:
174.129.228.67 - - [23/Oct/2011:06:56:53 +0300] "GET /robots.txt HTTP/1.0" 200 26 "-" "ia_archiver (+http://www.alexa.com/site/help/webmasters; crawler@alexa.com)"
The first thing I don't understand is why the strange requests don't include a method (get/post/head/etc). The second thing is obvious: what does it mean? And the third thing: why do I have different response codes for those requests? Sure, depending on what they do Apache replies differently, but I don't know what's behind the encoded requests.