Looks like Iranian Hackers Suspected in Recent Security Breach are either trying to get back for Stuxnet and more on Stuxnet. More likely it was for a man-in-the-middle attack to install viruses or trojan horse by posing as the actual company and uploading a compromised version of the software. The compromised software could make it easier to monitor social networking sites, etc.
Comodo, a digital certificate authority and security software maker, said on Wednesday that it unwittingly issued fraudulent digital certificates for Web sites operated by Google, Yahoo, Microsoft, Skype and Mozilla. Digital certificates are used to vouch for the authenticity of a site owner and facilitate encrypted communications between sites and their users. Comodo revoked all of the certificates immediately upon discovery of the incident and notified the site owners, the major browser makers and relevant government authorities, it said.