- Failing to install anti-virus, keep its signatures up to date, and apply it to all files.
- Opening unsolicited e-mail attachments without verifying their source and checking their content first, or executing games or screen savers or other programs from untrusted sources.
- Failing to install security patches-especially for Microsoft Office, Microsoft Internet Explorer, Firefox, and Netscape.
- Not making and testing backups.
- Being connected to more than one network such as wireless and a physical Ethernet or using a modem while connected through a local area network.
Source: Mistakes People Make That Lead to Security Breaches