Scan using any of the following:

1. Online scanner
-- Housecall:
-- ESET:

2. Malware scanner:
-- SUPERAntispyware:
-- A-squared Free:
-- Malywarebytes:

>>I thought the purpose of having AV was to prevent things from getting on your computer. Is that a naive assumption?
Depends on how the infection arrives. Depends on how the user respond. Not all type of risk and malware is detected by single scanner (free or paid scanners).