Spammers have begun taking advantage of Internationalized Domain Names as a home for penis pill portals and other spamvertised sites.
Internationalized Domain Names (IDN) allow domain names to include Arabic, Chinese and Russian characters, among others, as well as Latin letters.
The inclusion of non-Latin characters with domain names has been possible for several years, but it's only last year that some top-level domains were given internationalised versions, for example .рф for Russia.
Spammers have begun latching onto the availability of these services to establish spamvertised sites. One German language spam message intercepted by Symantec MessageLabs uses a URL shortening service to redirect to an IDN domain.
The spam message - advertising erectile dysfunction pills and supposedly linking to a Swiss pharmacy site - is nothing out of the ordinary, except for its use of Cyrillic domain names.
By using, in this case, a Cyrillic domain name, spammers may make it easier to register more convincing domains. The tactic may decrease hosting costs for penis pill merchants, as Nick Johnston, a senior software engineer at Symantec, explains.
"MessageLabs Intelligence expects the use of IDN in spam to increase in coming months, especially as it may be easier to find unregistered IDN domains," Johnston writes.
"Some registrars are likely to encourage wider adoption of IDNs and are expected to offer some registries at low prices, as we've seen with the introduction of other new top-level domains in previous years."
A blog post by Symantec, containing screenshots of the spam message and an explanation of the redirection techniques used in the scam, can be found here.
The more widespread use of IDNs in spam poses challenges for both brand protection experts and spam filtering firms, who may need to tweak their technology.
"The main impact of IDN on spam filtering depends on exactly how spammers use IDN," Paul Wood of Symantec MessageLabs told El Reg. "If spammers always include URLs in Punycode form (with a TLD of .xn--p1ai instead of the actual Cyrillic characters .рф) then spam filtering is relatively straightforward. Anti-spam software generally simply needs to be aware that xn--p1ai is a valid top-level domain."
"However, if spammers include IDN URLs not in Punycode, then it's likely that more work could be required, particularly given the various different character encodings that could be used to represent these characters. To convert to IDN, the characters would have to be converted to Unicode and then applying algorithms before finally doing Punycode conversion.
On the other hand, using IDN URLs in this way might harm a spammer's conversion rate due to legacy mail software and so on." ®