Twitter has been dealing with a denial of service attack this morning that has resulted in millions of users not receiving or posting tweets.

These days denial of service attacks typically are launched from botnets–large numbers of consumer PCs that have been infected with Trojans that wait to do the bidding of the “bot-herders” who manage them. The users of these machines may not know anything is wrong other than, “Gee, the Internet seems slow today.” Their Internet is slow because their computer is sending lots of traffic to the targeted site, in this case twitter.com. The bot-herders collect infected machines and then rent them out. Twitter is such a high profile site, it may be just a bot-herder or one of their customers wanting to show off the power of their bot net.

Is your computer a member of one of these botnets? It’s not easy for the average Internet user to find out. Seeing rapidly blinking lights on your cable modem even if you aren’t using your computer may suggest something is going on. But it could just be an updater downloading a new Firefox or operating system patch.

You may not be too worried about the state of Twitter. But you should Know that botnets can be told to do many things. They can be instructed, for example, to download keyloggers or other data stealing malware. The stolen data is then shipped off to collection servers where the bad guys can then use your bank username and password to steal money.

Keep your antivirus up to date and perform a full scan if you’re a little concerned.

Download and use SafeCentral if you want to bank and shop without the worry. SafeCentral users talk about this stuff here: community.safecentral.com.

Update:

It may be coincidental, but we saw a large increase yesterday in our virus-collection network. We received 200 times the normal average of emails with malicious attachments. One node, for example, went from 10 items to 2000 in a day. These were phony emails telling random recipients that a UPS parcel could not be delivered and asking the reader to “print out the attached invoice”. The attachment was not an invoice, it was a trojan.

Example of the email. Do not open the attachments in these emails if you get one!

• Denial of Service vulnerabilities back in the spotlight – patch BIND now!
  Until recently, only remote code execution vulnerabilities have made the mainstream news. These are the bug strains which may let an attacker get into your computer if you do nothing more than simply ...
• Outbreak: United Parcel Service notification malware attack spammed out
  Cybercriminals are attempting to infect computers around the world, disguising their attack as an email claiming to come from United Parcel Service about a parcel delivery. But this time they're not u...
• Outbreak: Post Express Service malware attack spammed out
  Sophos -- Be on your guard against the latest "undelivered package" malware attack that cybercriminals are spamming out right now. Regular readers of Naked Security will be all too familiar with em...
• Lil Wayne’s Twitter account shut down after hack attack
  Lil Wayne's Twitter account has been taken offline, after someone hacked into the popular rapper's account this weekend and posted a series of joke messages. A hacker, who seemingly guessed the singe...
• SonyEricsson WAP Push Denial of Service
  CSA DISCLAIMER: This video taken from YouTube. As well as any other video found on this site is not hosted here, it just embedded, and it taken randomly by our system from video hosting services lik...
• Twitter Trending Topic Attack (II)
  There was an attack targeting various trending trending topics on Twitter today. I’ve been analyzing the campaign and have collected the following information: (Malware and Maltego file available upo...
• Mozilla Firefox 3.6.12 Remote Denial Of Service, (Mon, Nov 15th)
  Thanks to our reader Seb for the heads up about a remote denial of service vulnerability within Firefox 3.6.12. There are a number of sites showing the exploit code which has been developed by an Ital...
• Symantec Guide to Scary Internet Stuff – No 6 Denial of Service Attacks
  The sixth video in the series explaining common internet security threats and how to avoid them, looks at one of the media's favourites.... denial of service attacks.....
• Cisco Security Advisory: Cisco IOS Software SIP (Session Initiation Protocol) Denial of Service Vulnerabilities – http://www.cisco.com/warp/public/707/cisco-sa-20100922-sip.shtml, (Wed, Sep 22nd)
  =============== Rob VandenBrink Metafore (c) SANS Internet Storm Center. http://isc.sans.org Creative Commons Attribution-Noncommercial 3.0 United States License. View full post on SANS In...
• Will Twitter attack drive off IT interest?
  This week's hack of Twitter probably won't prompt large companies to quickly abandon the microblogging site, but analysts said that further attacks could lead IT executives to start looking at alterna...