Hosted Anti-Virus is more secure
Hosted Anti-Virus is more secure and reliable than local machine software, because the virus never even gets to your PC and you are not responsible for regualr updates.
From Business and Finance
McAfee customers were left bewildered recently when their antivirus program began attacking legimate third-party applications as malware. The problem was caused by an update that McAfee issued for its popular antivirus software, with hundreds of executables wrongly flagged as W95/CTX, low-risk Windows 95 malware. Among the applications affected were Microsoft Excel, Flash, Google Toolbar and Adaptec drivers. McAfee published a list of about 330 programs known to have conflicts with the update, but experts have speculated that the true figure is much greater. Operating systems across the board were afftected by the mistake.
This is just one example of the many ways local Anti-Virus software can let you down. The primary issue of course is that unless you are in a highly controlled corporate IT environment, the responsibility for protecting your computer is actually yours - not the anti-virus software provider. This is because you must make sure the software is up to date with the latest definitions.
Hosted Anti-Virus is by no means perfect … since it really only protects your email … but the majority of incoming files to your PC do originate via email. If you protect your email service with a hosted anti-virus service, any infected mails will be detected and quarantined before they ever get to your machine, preventing any threat of an infection.