Mejor antivirus gratuito

Tenía instalado el avast! (recomentadión de Sergio, informático, como no!), después de usar el AVG.

El caso es que he tenido un problema con el avast! y me he dicho, vamos a buscar otro, a ser posible el mejor. Tras poner en google "best free antivirus" me he encontrado con una tabla que me ha ayudado a elegir (espero que sea fiable):

Product	malware on demand	adware / spyware on demand	false positives	scan speed	proactive detection	response times	malware on demand	adware / spyware on demand
AntiVir (Avira)	++	++ (4)	+	++	+	++	99.8%	99.0%
Avast! (Alwil)	++	++	+	+	o	o	99.3%	98.3%
AVG	+	- (4)	+	+	o	o	95.8%	87.0%
AVK 2008 (G Data) (1)	++	++	o	-	+	++	99.2%	99.1%
AVK 2009 (G Data) (2)	++	++	+	+	++	++	99.8%	99.8%
BitDefender 2008	+	-	+	-	++	+	97.7%	87.8%
BitDefender 2009	+	-	+	o	++	+	97.6%	88.0%
CA-AV (VET)	--	--	++	o	-	--	65.5%	68.0%
ClamAV	-	o	-	--	-	++	88.5%	92.8%
Dr Web	--	-	o	o	+	o	84.9%	89.6%
eScan	+	+	o	-	+	++	97.8%	97.4%
Fortinet-GW	o	--	o	+	++	+	92.6%	81.9%
F-Prot (Frisk)	o	o	+	+	o	o	94.8%	92.6%
F-Secure 2008	++	++	+	o	++	+	98.2%	98.4%
F-Secure 2009	++	++	+	+	++	++	99.2%	99.6%
Ikarus	++	++	o	+	+	+	99.5%	98.6%
K7 Computing	o	o	o	++	-	o	92.1%	94.0%
Kaspersky	++	++	o	o	+	++	98.4%	98.3%
McAfee	o	o	++	o	+	-	93.6%	94.5%
Microsoft	+	+	++	o	-	-	97.7%	97.1%
Nod32 (Eset)	o	o	++	++	++	+	94.4%	94.7%
Norman	+	+	+	o	+	o	96.3%	95.8%
Norton 2008 (Symantec)	+	o	++	+	+	o	97.8%	94.6%
Norton 2009 (Symantec)	++	+	++	++	+	++	98.7%	95.4%
Panda 2008	-	o	+	+	++	o	86.4%	93.4%
Panda 2009	o	+	+	+	++	+	91.8%	95.6%
Rising	--	--	+	o	o	o	83.4%	77.5%
Sophos	+	+	+	+	++	+	97.5%	95.0%
Trend Micro	o	-	+	+	o	+	91.3%	88.5%
TrustPort	++	++	-	--	++	++	99.5%	98.4%
VBA32	o	-	o	o	+	o	90.5%	85.2%
VirusBuster	-	-	+	+	o	o	89.0%	85.8%
WebWasher-GW (3)	++	++	o	++	++	++	99.7%	99.2%
ZoneAlarm	+	+	o	o	+	++	97.8%	97.7%
Index	malware on demand	adware / spyware on demand	false positives	scan speed	proactive detection	response times	malware on demand	adware / spyware on demand
++	>98%	>98%	no FP			<>
+	>95%	>95%	1-2 FP			2 - 4 h
o	>90%	>90%	3-4 FP			4 - 6 h
-	>85%	>85%	5-6 FP			6 - 8 h
--	<85%	<85%	> 6 FP			> 8 h

Notes
(1) AVK 2008 uses the Avast and Kaspersky scan engines
(2) AVK 2009 uses the Avast and BitDefender scan engines
(3) WebWasher uses the Avira engine and a self-developed heuristic engine
(4) the free (personal) edition does not include ad- and spyware detection, so the results would be --

Así que finalmente estoy instalando el primero de la lista en su versión gratuita: Antivir (avira)

Pantallazos (screenshots):

Fuente | Tabla | Antivir (descarga)