Many people today send and receive e-mails in HTML format. It’s nice to look at, you can format it easily, you can add pictures and more. In fact, when you read an HTML e-mail, you’re effectively reading a web page … and therein lies the problem!
There’s no shortage of vulnerabilities in IE, many of which have been exploited by viruses, worms and Trojans over the last few years. And the ‘lead-time’ between the discovery of a vulnerability and the appearance of an exploit that targets it has become progressively shorter.
So HTML is intrinsically insecure. Even if an HTML e-mail looks like regular text, it may be more than that. It’s possible to embed script within it that will execute automatically [including exploit instructions]. This may harm your machine directly or leave it open to attack.
Recent reports suggest that ‘phishers’ have started to make use of HTML e-mails. In a ‘classic’ phishing scam, the user receives an e-mail that is made to look like it has come from their bank. There’s a link to a web site that’s designed to look like their bank’s web site. The user is prompted to input their personal details, which are then captured by the phisher. Of course, in order to succeed, the scam requires an unsuspecting user to click on the link and enter their details.
Now, however, it seems that phishers are trying to ‘cut out the middleman’ and launch the fraudulent web site automatically. This is done by sending an HTML e-mail containing hidden script instructions designed to edit the user’s hosts file. So when they next try to access their bank, they are re-directed to the fraudulent web site.
One more reason to use plain text e-mail, rather than HTML, and to disable scripting on your machine.