Antivirus and antispyware are reliable only if they are updated regularly.
Note that most of current anti-virus software updates automatically via the Internet.
The free, lightweight, and attractive Panda Free Antivirus is one such utility.
However, its scores in independent lab tests and our own tests have dropped since my review of the previous edition.
In our environment we have automatic updates turned on for Panda. However, some times there are a few machines where the Agent version will update but the Protection version won't. Then the only solution is to uninstall and reinstall Panda on those machines because it will say the signature file and everything else is up to date when syncing.