今回も長くなったことと、新たな視点だと思ったので書き起こします。
技術系サラリーマンの交差点: メールからIPアドレスがわかることも多いらしい
元記事で、POP と言われているのは SMTP のことですね。
メイル送信時の IP アドレスですが、SMTP サーバというものが受信した時点で送信元のアドレスを Received として付与します。
このアドレスは基本的に詐称できません。
ブラウザから送信するタイプのメイラでも端末の IP アドレスは大抵(独自)メッセージヘッダに記載されます。Hotmail も Yahoo も送信元 IP はわかります。
過去はダイヤルアップ接続がメインであり、接続のたびに IP アドレスが変化していたため、せいぜいプロバイダと地域までしか解りませんでしたが、現在の ADSL などの固定IPアドレスの世の中になると IPアドレスと個人の結びつきが強くなる、という件は実際に危惧されてもいます。
IPv6 に関しても真っ先にこの点が議論されていますし。
でも、ダイヤルアップであってもプロバイダが調査すれば送信*者*の特定は可能です。そうでなければ犯罪天国になってしまいます。完全匿名を許したらインターネット社会が成り立たなくなります。2ch が後になってログを記録するように変えさせられた通り。
一般的には端末のIPアドレスが一定以下の間隔で変化すれば充分とされており、ADSL などは怪しいですが、逆に企業内からなどの場合は、並列化された中継(HTTP/SMTP)サーバが利用されたりするので、どの企業かは分かってもその中の誰かは外部からは突き止めるのが困難です。
メイルを送信した端末のIPと HTTP アクセス時の proxy サーバが付与する端末の IP を突き合わせれば、企業内からであってもメイル送信者と Web アクセス者が同一であるかを推定することができます。でも、企業の proxy サーバでは内部の端末のIPは送出しないことが多いと思いますが。
(追記)この段落、若干編集しています。
でもまぁ、これを気にする方は、もう Web で見つけた人とのやりとりはやめるしかないでしょうね。
ところで、Web バグ(参考1)というものが存在します。電子メイル送信相手に気付かれないようにWebにアクセスさせる事で、送信先メイルアドレスとIPアドレス、およびクライアントパソコンを識別するID(cookie による)を紐付けすることができます。HTML メイルから参照される画像が自動的に表示される環境では、プレビューするだけで実行されます。
Web バグでは、それが生きているメイルアドレスか?そこから辿って商品を購入したか?ある消費活動を行った人のメイルアドレスは?といった事が収集されます。
今回の話はマーケティングという側面ではなく、個人間のやりとりに関する話ですが、上記から言えることは、メイルアドレスを知っている人間の自サイトでの活動を追跡しようと思えば、その相手からのアクションを待たずとも可能である、ということです。しかも IP アドレスよりも確実な cookie に設置した ID によって。
cookie をオフにしていてもクライアント IP アドレスは採取されます。
さらにこれに「名寄せ」を加えれば、住所氏名などの個人情報まで結びつく可能性もあります。これは業者の協力が必要でしょうけれど。
こちらも回避しようと思うならば、そういう事をする可能性のある Web サイトを見てはいけません、ということになるでしょう。
HTML メイル、あるいはそこからリンクされる画像などを表示する設定をやめる事で、無意識のうちに追跡される可能性は減らすことができますが。
結局、好奇心とリスクのトレードオフで、各自が判断するしかないわけですが。
念のためですが、私は Web 閲覧行動に関してリスクはあまり感じていません^^;。
でも、人によっては(特に女性)リアルワールドにも影響を及ぼすようなリスクも考えられないわけではありません。
やはり、好奇心、というよりサイト管理者への信用でしょうかね。
参考1:はてなダイアリー - 高木浩光@茨城県つくば市 の日記:Webバグについて復習する
参考2:EarlGrey Tearoom: HTMLメールは、IPアドレスを通知する

なるほど、
と言っても30%程度しか理解できないですが。
パソコンって便利で楽しいですけど、いろんな問題を抱えているようですね。
ちょっと手直ししたいんですが電車の中、且つ打ちあわせなので出来ず_o_。
当記事の趣旨は、「だから気にしだしたらきりがないよ」ってことです^^;。
後でフォローできればと思います。それまでツッコマブルなままでもいいや^^;。
ウチみたいに完全固定IP、WHOIS で個人名まで出る場合はもう(w。
いろんな所に足跡残しまくってる、と:p。
# keisuken さんの場合は足紋、ですかね^^;。
足跡すら雑踏に埋もれさせたいなら匿名プロキシを一生懸命探すしか…。足跡を残したくないならアクセスしないか RSS reader をうまく使うか…。
でも足跡(たとえ足紋であっても)を見られてどんな害があるのかはなんともですが^^。
「あぁ今起きてるのね」程度なのよね…。
そんなわけで、起きてるのよという足跡… -_-
明日、、てヵ今日ヵ・・・
10時半には家出しないといけないんだけど、
今から一回寝るべきか、ずっと起きとくべきか、
悩んでおります。
と、いいながら起きてるじゃん。
焼き肉のジャン。
大桃美代子でも見ながら朝食でもとって、
その後のコトでも考えるヵ・・・・
ずぅ~~~~~~む、ぽん!
って、ぽんじゃねーーよ!!
#はぁ~~~~~ -_-
>足跡すら雑踏に埋もれさせたいなら匿名プロキシを一生懸命探すしか
実は、匿名プロキシ使っている人なんてかなり限られているので、匿名プロキシを使った人、ということでより特定し易かったりもするのよね~:p
まぁ、ほんとに女性とかならどうしたらいいんだ、というのは真面目に考えると難しいですけど…。
NK9rOt
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