Need a good reason to justify not accessing the Internet with your DAW?
Antivirus programs tether the performance of your computer [to] that of one three years its elder.
In other words, anti-virus software will kill the performance of your finely tuned digital music workstation.
(It should go without saying, but this is also a good reason not to fill your computer with audio applications of unknown provenance. For example, that $3000 plugin package you found on PirateBay.)