According to Google's Diagnostic page for opexpert.com, OpExpert

What happened when Google visited this site?
Of the 2 pages that we tested on the site over the past 90 days, 2 page(s) resulted in malicious software being downloaded and installed without user consent. The last time that Google visited this site was on 2010-05-06, and the last time that suspicious content was found on this site was on 2010-05-06.
Malicious software includes 1 trojan(s).

Malicious software is hosted on 2 domain(s), including invosterina.com/, chickfilapoplar.com/.

1 domain(s) appear to be functioning as intermediaries for distributing malware to visitors of this site, including greatbussinessite.com/.

This site was hosted on 1 network(s) including AS6245 (NETWORK).

Has this site acted as an intermediary resulting in further distribution of malware?
Over the past 90 days, opexpert.com did not appear to function as an intermediary for the infection of any sites.

Has this site hosted malware?
No, this site has not hosted malicious software over the past 90 days.

How did this happen?
In some cases, third parties can add malicious code to legitimate sites, which would cause us to show the warning message.

Next steps:
Return to the previous page.
If you are the owner of this website, you can request a review of your site using Google Webmaster Tools. More information about the review process is available in Google's Webmaster Help Centre.