Which are the biggest security threats on the web?

There are so many new threats coming up daily but viruses still can wreak havoc in a company's network by infecting files and applications, costing a company thousands of dollars of lost production time. Viruses such as Parite, first detected in October 2001, infects its host file, Netsky, and drops executable malware. Other viruses, such as Virut, are polymorphic file infectors that download and run other malicious programs meanwhile infecting all the executable files in order to replicate.

In a phishing attack, users will generally be enticed with an alluring e-mail subject line, often touting a fake breaking news headline or a celebrity video. Once the e-mail is opened, the user is treated to a brief message, and encouraged to click on a malicious link embedded in the message claiming to lead to another web site or video. Instead, the link often links to an infected web page, which installs malware on the unsuspecting user's computer.

As like you told there are so many security threats on the web like spams,scams, phishing, unlawful entry, espionage, identity theft, financial theft etc.All types of security threats include data leakage except denial of service beacuse its an attack on availability.In last 5years,around 500 million records containing personal identifying information of United States residents stored in government and corporate databases leaked.In that 300 million,happened based on the above mentioned threats.

So we cant tell  exactly what are all the biggest threats.

Keyloggers and Trojans which hijack your userids and passwords, and hijack your system to make your computer as one of the nodes in a large network to upload files, send spam mails etc without your knowledge. Just watch your lan/internet connection and you will find continuous traffic from your system. It is observed even anti-virus and messenger clients are hijacked to add a pipe to take control of your system. Test with Netlimiter utility and findout how many ports are  operating in your system and data upload when you are not sending anything out.  http://www.netlimiter.com/download/nl_2010_mon.exe

n the last five years, approximately 500 million records containing personal identifying information of United States residents stored in government and corporate databases was either lost or stolen.  Since little attention was given to database breaches prior to 2005, it is safe to assume that every man, woman and child has had their personal information exposed at more than once.  In fact, many citizens have received multiple notification letters informing them that their personal information has been lost or stolen.

We will likely see 2009 security breaches resulting in the same past practice where security breach notification letters will insist there is no evidence the breach has resulted in any harm. Unfortunately, there is no longer any doubt that personal information stolen from databases is being used by organized identity thieves to commit crimes involving identity fraud. 

AS of today date there are about 260 odd data breaches which are publised  - Most of the data breches are from lost or stolen mobile devices

Third world war may take place in web

According to a research  there are 800 million  malware's altough not sure which ones to mention. Virus,Worm,Trojan leads the way.

i think it will be one of the most concerned threat to deal with because techy people like u and me are aware of the fact but people who are from different sectors and use their computers just for may be emails chat productivity work are not aware this threat if a a person who does most of his transaction online and receives an email asking to update his credentials on his bank website and gives a fake link to a fraud bank website how a non tech savvy person is going to deal with it and i have working in a tech support for so long and mostly for western continents where internet is the most basic and essential part of their life and something which they cannot live without, itself create a question about how to deal with as it is very difficult to track down these threats....