This is specifically Microsoft and Windows OS related, rather than architecture related. It isn't particularly relevant these days anyway (if ever!) as 64 bit is standard.
Security was used as an issue to help market the 64 bit version of Windows 7 OS a few years back by saying the version had a lower rate of infection than 32 bit versions. They claimed this (mainly) because the ocean of viruses and malware written into 32 bit device drivers don't work in a 64 bit environment. The Windows 7 hardware was also harder to exploit with DEP turned on and Patchguard included. Device drivers needed signing using certificates from trusted issuers.
At the time, using 64 bit Windows offered a slight reduction in infection potential, but that never really meant you were totally safe without protection anyway. Even at the time, there was still a mountain of malware and viruses that COULD infect 64 bit Windows OS systems, even if they didn't load with via a device driver. Of course, there have been a million plagues more written for Windows OS's since, including 64 bit versions!
