Web rep is a controversial service, where it depends on user input. At best it is a guidance where not to go because content might be questionable, worst case scenario it can be used to get users on a wrong footing. But a lot of these services mix web rep and security alerts, so users may get the wrong idea of what it is for. It was started with the now discontinued Scandoo service, a search engine ranking service. Then came SiteAdvisor, now sort of been run into the ground after McAfee took over. Webutation gives Google Safebrowsing results (loads and loads of pages not yet scanned or ranked, just like at NSW), Website antivirus info on status pop-ups, downloads, links, OT results and GRated/Child Safety.
But there are also sites that rank the following: technical info like htp Cookies, P3P or not,
Dynamic Content info - header info, Server details (exploitable), Browserscripts, Java Applets, Siverlight or not, Adobe Flash or not, Youth Content Filtering, Spamcheck, Safe Browsing status, WOT, Alexa rank, Wikipedia links, link analysis,
DrWeb url checker misses a lot because it cannot scan deep enough, and is dependent on what is in the engine database. Bitdefender Traffic Light has an advanced Phishing Filter, a malware filter, search results analyzer and antifraudfilter to be brought in. Better than WOT that has been poisoned with particular user data.

Another mixed real-time pre-scan extension is M86 secure browsing. It is not one of the worst scanners, a pity it is not available for Google Chrome (IE and Fx extensions)

There are discrepancies in the scanning results of the various Web rep extensions/tools.

I’d rather have something like Google Safebrowsing with a good combined badware buster etc. sinkhole implementation. In the situation we have now I have to combine the results of various URL scanners, VT scans, wepawet scans, iFrame scanners, sitecheck sucuri free website scan, SOSWebScan etc. to have a bit of a clue where not to click and still there is a minefield open to us of just hacked reputable sites, zeroday script exploits.

What remains is in-browser protection like NoScript/RequestPolicy in Fx and similar protection for GoogleChrome NotScripts/Better Pop up Blocker, Blocker extensions then you also will steer clear even from future exploits, because they cannot run inside the browser. Of course sandboxing also helps to this effect.

What is web rep? A bit of guidance, at best mixed with some snake oil reliability, for the average user that clicks after all he/she/it can click on, there is not an easy remedy, the problem stays between the link and the chair…

polonus