Facebook, the world’s largest social-networking web site, on Wednesday acknowledged an outburst of spam attacks.

“Facebook has been fighting mounting security threats in recent weeks … we have received reports from users of spam and phishing attacks,” the company said in a statement.

The attacks were caused by a worm called Koobface, referred to across social sites as the Facebook or MySpace worm. The Internet worm began across MySpace and Facebook in July. Anti-virus firm Kaspersky Lab has identified about 27 Koobface variants.

The hugely popular Palo Alto, California, startup had managed until now to remain relatively spam-free, with less than .002 percent of people on Facebook having received spams, the company reported in July. Facebook announced a series of measures to eradicate the new problem.

“We have detected and contained a worm. We are investigating every report, removing false content, blocking bogus links, and addressing the concerns of our users. These efforts have limited the affected users to a small percentage of those on Facebook,” the company said in a statement.

The company is also asking that users report any type of unusual messages sent through chain letters, applications, or on the their Wall–an application allowing Facebook users to send messages to each other in the form of text, picture, and video.

Some of the attacks reported by users include hijacked accounts or viral messages such as “Paris Hilton Tosses Dwarf On The Street; Examiners Caught Downloading Grades From The Internet; Hello; You must see it!!! LOL.

The startup is taking the matter seriously. The company sued alleged Facebook account hijacker Adam Guerbuez last week.

The social-networking giant, which was founded four-and-a-half years ago and rose to the top at a tremendous rate, is one of the most enticing online targets for experienced or wannabe hijackers.

Facebook has tripled in size since the same time last year.  In April it grabbed the No. 1 spot from social-networking rival MySpace. The company on Monday announced  it has 100 million registered users.