On a computer running Microsoft Windows, it is important to have up to date anti-virus software that has not expired. Many manufactured Windows machines come with a trial version of anti-virus such as Norton or MacAfee, we recommend setting up a subscription or removing this software and installing a free one.
For home and small business computers we recommend this free Anti-Virus Microsoft Security Essentials.
If you prefer a lightweight paid for Anti-Virus we've had great luck with Nod32.
CalTel recommends but does not support 3rd party software. Please contact the software developer if you experience problems.