Hola he eliminado el tema anterior que contenía el mismo mensaje.
Echale un ojo a esto, explica un poco como funciona:
http://en.wikipedia.org/wiki/Blackhole_exploit_kitBasic summary of how Blackhole works
1. The customer licenses the Blackhole exploit kit from the authors and specifies various options to customize the kit.
2. A potential victim loads a compromised web page or opens a malicious link in a spammed email.
3. The compromised web page or malicious link in the spammed email sends the user to a Blackhole exploit kit server's landing page.
4. This landing page contains obfuscated javascript that determines what is on the victim's computers and loads all exploits to which this computer is vulnerable and sometimes a Java applet tag that loads a Java Trojan horse.
5. If there is an exploit that is usable, the exploit loads and executes a payload on the victim's computer and informs the Blackhole exploit kit server which exploit was used to load the payload.
Defenses against the Blackhole exploit kit
A typical defensive posture against this and other advanced malware includes, at a minimum, each of the following:
* Ensuring that the browser, browser's plugins, and operating system are up to date. The Blackhole exploit kit targets vulnerabilities in old versions of browsers such as Firefox, Google Chrome, Internet Explorer and Safari as well as many popular plugins like Adobe Flash, Adobe Acrobat and Java.
*Running a security utility with a good antivirus and good host-based intrusion prevention system (HIPS). Due to the polymorphic code used in generating variants of the Blackhole exploit kit, antivirus signatures will lag behind the automated generation of new variants of the Blackhole exploit kit, while changing the algorithm used to load malware onto victims' computers takes more effort from the developers of this exploit kit. A good HIPS will defend against new variants of the Blackhole exploit kit that use previously known algorithms.
Puede haber sido por desactualización del navegador, java, flashplayer...
Actualiza todo, vectores de ataque hay bastantes, si puedes migrar a la última versión también te iría bien.
Por la fecha de modificación de los ficheros puedes guiarte un poco, no en todos los casos se modifica ese dato para ocultar una modificación.
Saludos.
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lo corregí asl ver tu comentario, no me había fijado 
