Researchers at Symantec caught spammers using a new technique to obfuscate URLs.
Spammers have traditionally tried to obfuscate e-mail headers or bodies to sneak past filters.
"So far, we have seen the use of non-ASCII characters or special characters that are not seen in legitimate URLs to obfuscate the domains or links in the spam messages," blogged Samir Patil, a security analyst at Symantec. "With such obfuscation in place, content-based antispam filters have limited success against such variations."
Now, spammers are using the soft hyphen, a graphic character imaged by a graphic symbol identical with or similar to the hyphen (-).
"It is used when a line break has been established within a word," Patil wrote. "In HTML4 standards, the soft hyphen is represented as "". The shy character is ignored by many browsers (for example, Firefox 2 ignores this character), unlike in Microsoft Office documents and in a small number of browsers in which the shy character visible and is treated as a normal hyphen."
According to Symantec Abuse Desk Analyst Eric Park the volume of spam using these attacks is "pretty low."
"I looked at the past three days worth of messages containing the soft hyphen in the URL," he said. "It really varies from "injury lawyer" [spam] to penny auction promos to window replacement. These are typical topics associated with hit & run/snowshoe spammers. For instance, these guys don't send meds spam."
Park said he couldn't tell what groups or botnets the spam may be associated with.