The purpose of this agency is to prevent harmful individuals and substances including terrorists, criminal illegal Simmigrants, drugs, weapons harmful pests and diseases, and other contraband from entering the United States: Immigration and Naturalization Services Immigration and Customs Enforcement Department of Homeland Security Customs and Border Protection

## Step 1<br />The problem is asking us to identify the U.S. agency that is responsible for preventing harmful individuals and substances, including terrorists, criminal illegal immigrants, drugs, weapons harmful pests and diseases, and other contraband from entering the United States. <br /><br />## Step 2<br />We have four options: Immigration and Naturalization Services, Immigration and Customs Enforcement, Department of Homeland Security, and Customs and Border Protection. <br /><br />## Step 3<br />The Immigration and Naturalization Services primarily deal with lawful immigration and citizenship issues. <br /><br />## Step 4<br />The Immigration and Customs Enforcement focuses on the investigation and enforcement of federal laws governing border control, customs, trade, and immigration. <br /><br />## Step 5<br />The Department of Homeland Security is a cabinet department of the U.S. federal government with responsibilities in public security. <br /><br />## Step 6<br />The Customs and Border Protection is the largest federal law enforcement agency of the U.S. Department of Homeland Security. It is tasked with securing the U.S. borders. <br /><br />## Step 7<br />Given the description in the problem, the agency that best fits the description is the Customs and Border Protection. This agency is responsible for preventing harmful individuals and substances from entering the United States.