According to studies, spam accounts for about half of all emails received. Spam was once seen as a minor nuisance but has increased to the point where many users have lost confidence in email's effectiveness due to viruses spread through unsolicited messages. In 2003, the US passed the CAN-SPAM Act to set standards for commercial emails by prohibiting fake headers and requiring opt-out. However, spam increasingly originates from outside the US where these laws do not apply. The top ways to protect against spam include avoiding publicly listing your email, using spam blocking software, maintaining separate addresses for different purposes, avoiding unknown attachments, and using email services with bulk mail filtering.