For years, security vendors have warned users to be careful about unsolicited emails. Clicking on embedded links in these emails, they say, could be dangerous, as could opening attachments that come with them. That includes emails purporting to be from couriers such as DHL and UPS, which could in fact come from malicious hackers and have attachments that are actually malware. In June, malware found in some of these attachments was a variant of the Kryptik Trojan, AppRiver warned.