問65
頻出度★★★
電子メールを介したウイルスの被害に遭わないために注意すべきこととして, 適切なものだけをすべて挙げたものはどれか。 a 信用できる人からの電子メールであっても, 添付ファイルのウイルスチェックを行う。 b 添付ファイルの種類が音声や画像などの非実行ファイルであっても, ウイルスチェックを行う。 c 不審な電子メールは, メールソフトのプレビュー機能で内容の安全性を確認してから閲覧する。
平成23年度 特別試験 ITパスポート試験 問65
This question's explanation and your answers so far.
解説
問 65
- ア
正解 The correct answer is ア. Only a and b are appropriate. First, regarding a, an email virus may use the recipient address book to send itself to acquaintances without the infected person noticing, or it may arrive disguised as a trusted party through spoofing of the sender address. In other words, who the mail came from is no guarantee at all that the attachment is safe, so performing a virus check on the attachment even when the mail is from a person you trust is appropriate. Next, regarding b, non-executable files such as audio or images look safe at first glance, but there is a technique of faking the file extension so that the file is in fact an executable, and there are also cases where malicious data that exploits a vulnerability in the application opening the file is embedded in an image or document data file itself, so that a malicious program starts running the moment the file is opened. Therefore performing a virus check regardless of the type of file is appropriate. On the other hand, c is clearly wrong: the preview function automatically interprets and displays the body of a message without any action to open it, so a script or a malicious tag embedded in an HTML mail, or external content that is loaded automatically, can run and infect the machine merely from previewing. Far from being a way to confirm safety, it can itself become the trigger for an infection, so the correct handling of a suspicious email is to delete it without opening it, preview included. Hence only a and b are appropriate, and ア, which lists exactly those and nothing else, is the correct answer.
Incorrectイ
This option is wrong in treating a, b and c as all appropriate. The judgments on a and b are correct, but c, which says to use the preview function of the mail software to confirm the safety of the content of a suspicious email before opening it, is not appropriate. Preview is a mechanism that automatically interprets and displays the message body, so a script planted in an HTML mail can already run before the message is read, which means preview cannot serve as a way to confirm safety. Because it includes the inappropriate c, this option does not satisfy the condition of listing only and all of the appropriate items.
Incorrectウ
This option makes two mistakes: it drops the appropriate b and includes the inappropriate c. Even for non-executable files such as audio or images there are attacks that fake the file extension or exploit a vulnerability in the file format, so b is an appropriate measure that calls for a virus check and must not be excluded. In addition, counting the confirmation of safety by preview (c), which can itself become the trigger for an infection, as appropriate is also wrong.
Incorrectエ
This option makes two mistakes: it drops the appropriate a and includes the inappropriate c. A virus may abuse the address book of an infected person and arrive while impersonating an acquaintance, and the fact that the sender is someone you trust guarantees nothing about the safety of the attachment, so a is a necessary measure and cannot be excluded. In addition, regarding the confirmation of safety by preview (c) as appropriate is also wrong.
ここがポイント
- The principle of protecting against email-borne viruses — an attachment must always be virus-checked, no matter whether the sender can be trusted and no matter whether the attachment is in an executable format. A virus may arrive disguised as a trusted party through spoofing or through abuse of an address book, and there are also attacks that fake the file extension or exploit a vulnerability in the application that handles a data file such as an image, an audio file or a document, so safety must not be judged from appearance.
- The danger of the preview function — the preview (preview pane) of mail software is a function that automatically interprets and displays the message body, so a script planted in an HTML mail or external content that is loaded automatically can infect the machine merely from viewing it. It therefore cannot serve as a way to confirm safety; the correct handling of a suspicious email is to delete it without opening it, preview included. Learn this together with keeping the virus definition file up to date as a basic countermeasure.
用語