I used to love AVG. It used to be lightweight and do a decent job. Now it's jumped on the bloatwagon and the fact that twice it flagged critical Windows files as viruses and deleted them, causing many Windows users to be unable to boot to Windows has soured me off of them for good:

http://en.wikipedia.org/wiki/AVG_(software)

<span id="Issues" class="mw-headline">Issues</span><ul>[*]When uninstalling AVG version 7 or 8 in Windows XP/Vista and attempting to install other anti-virus programs such as <font color="#0645ad">Kaspersky Anti-Virus</font> or <font color="#0645ad">Norton AntiVirus</font>, the latter programs will not install. Instead, they show an "incompatible software installed" error even if the uninstalled software has been removed using the control panel. This happens because software that updates and changes can add registry entries that were not added when the product was originally installed (therefore the uninstaller is unaware of the registry keys).<sup id="cite_ref-19" class="reference"><font size="2"><font color="#0645ad"><span>[</span>20<span>]</span></font></font></sup>[*]A signature update dated November 9, 2008, crippled some computers, as it allowed the software to treat "user32.dll", a major component of Windows XP/Vista, as a trojan and advised users to delete it. Users who deleted the file in question were put on a continuous reboot loop. The problem was rectified a few days later with a new signature database and further safeguards were added to the product (270.9.0/1778).<sup id="cite_ref-20" class="reference"><font size="2"><font color="#0645ad"><span>[</span>21<span>]</span></font></font></sup>[*]Towards the end of July 2009, a software update caused the program to inform users that <font color="#0645ad">iTunes</font> was infected<sup id="cite_ref-21" class="reference"><font size="2"><font color="#0645ad"><span>[</span>22<span>]</span></font></font></sup> with a non-existent virus, Small.BOG. If users followed the recommended instructions, it would remove critical DLL files and corrupt the iTunes installation.<sup id="cite_ref-22" class="reference"><font size="2"><font color="#0645ad"><span>[</span>23<span>]</span></font></font></sup>[*]An update of AVG 2011 resulted in Windows 7 64-bit systems being <font color="#0645ad">bricked</font>, leaving machines in a continuous reboot loop. The update has now been removed.<sup id="cite_ref-23" class="reference"><font size="2"><font color="#0645ad"><span>[</span>24<span>]</span></font></font></sup>[/list]Sorry, linked to different stories to the same instance, updated my links