Answer Best answer as chosen by user CIT-IT
Dont uninstall Trend-Micro before uninstalling AVG!
Because anti-virus & firewall programs must intercept fundimental system calls (i.e.: disk I/O's, browser/network events, etc.) to perform their checks they must add 'hooks' into the OS at a very basic level ... in fact, they may actually replace registry entries and/or .DLL's, .EXE's, etc, in the operating system's root libraries (i.e.: Win-7 runtime files).
When a second anti-virus program is installed (i.e.: AVG) it will want to catch many of the the same events; thus, it will undoubtably alter some of the 'hooks' (files, etc) that were already altered/replaced by the first anti-virus program (i.e.: Trend-Micro).
If you uninstall the first anti-virus program (i.e.: Trend-Micro) without having uninstalled the second one (i.e.: AVG), the uninstall process may actually overlay some of the 'hooks'/files/etc just (re)altered by AVG with what Trend-Micro saved off (the original OS settings & files); thus, hosing over both AVG and Win-7 ... you'll end up with a mix of things altered for AVG and things AVG expects to be altered but that are now back to the original Win-7 settings. Net result: You may to have to re-install the whole OS to get back to a fully functioning OS!
The same can happen regarding firewalls (and any other software that requires tight intregration into the OS). Two (or more) at a time can be very, very dangerious come uninstall time and they can also compete for resources and/or 'confuse' each other, etc, when both are running. For instance: "Deadly Embraces" (system lock-ups) can occur when both products try to handle the same event at the same time, etc.
So ... to be safe, fully uninstall an undesired product (& make sure your system still works propertly) before you install a replacement product ... This is a very good rule of thumb for all (replacement) software product installs actually.
Since you already have both Trend-Micro & AVG installed, I suggest you uninstall them in the reverse order installed and then re-install only the one you want (i.e.: uninstall AVG, reboot, check out system, if OK uninstall Trend-Micro, reboot, check out system, if OK install AVG).
1) It is not a bad idea to create a recovery point before/after any anti-virus/firewall/etc install either.
2) Most anti-adware/spyware programs do not alter the OS, etc, UNLESS they also have a 'active' protection/screening processes that run anytime your browser is open for instance (i.e.: something intregrated into the browser as an add-on, etc). Most of the time, multiple 'stand-alone' (or on-line) scanners run outside of the OS/browser will not hurt the OS.
Just sayin' ...
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