Researchers at Sucuri are monitoring a rise in website compromises in which visitors are redirected to domains that offer to sell Windows product keys.

In a new blog post Wednesday, the security company detailed its investigation of an unnamed WordPress website whose core files were hacked for this very purpose, noting that the attack used a code injection designed to avoid detection by search engines that might otherwise blacklist the site or warn users of a potential hack. In this instance, users were taken to malicious domains that offered a “Windows 8.1 Product Key Generator 2016 Download.”

“In order for hackers to keep their campaigns profitable, they must make the spam content invisible to search engines,” reads the blog post, authored by malware analyst and team lead Bruno Zanelato. “To prohibit Google from flagging the content as malicious, the code tries to avoid being discovered entirely.”