What 0x90.se is

0x90 is the main initiative by Thomas a.k.a Circle and we are a loosely knit number of ethical security professionals mainly located in Sweden. We are not a fixed group and may vary in number of members depending on interest, time and such. However, a few of us has been around in this area for well over 15 years!

We are trying to focus this site on a wide range of areas, both technical and non-technical security in an attempt to reach as many readers as possible. You could say that this site was born out of frustration, as we feel that the area of information and IT security in large is not being focused upon as it should be. Most individuals and many organizations lack essential knowledge in this area and are oblivious about what is going on out there. If we don’t react soon, we will fall further behind, in a world where cyber crime is getting more and more sophisticated and gaining more and more economical muscle.

What 0x90.se isn’t

You will not find any material on this site that will conflict with Swedish law. Also, we will not assist you in hacking, cracking or any other illegal activity. So please do not bother asking such questions. Should you find information that do conflict with Swedish law, please contact us as soon as possible so we may remediate the issue as soon as we can.

The information and the files available on this site may not be used in any illegal activities. The site owner, its members and co-writers cannot be held responsible for any illegal activites performed using information/data/programs/tools etc. from this site. Please check your local laws before using any of the tools, instructions or similar.

0x90 Fun Facts

CPU Instruction – 0x90 is the hexadecimal representation for the Intel CPU instruction: NOP – No Operation. Many know of this, however, fewer know that NOP is only the short representation for the assembly instruction: XCHG EAX, EAX which in turn does absolutely nothing.

0x90 as hostname – This is one of my favourites! I’ve been playing with this one for at least 16-17 years on my computers. If a system has a hostname in the form of a hexadecimal number, for example 0x90 and you try to ping it by its hostname from Windows, you will get quite fun results 😉 In the case of 0x90, this hostname resolves to IP address: 0x91 will resolve to and so forth. As you can imagine, this will drive some administrators nuts!


You may contact us using the email address below. You may also contact any of the writers personally, using his/her alias instead of “info” as shown below. However do note that we may not be able to get back to you as we all lead very busy lives, so don’t think that we are rude or something. If you feel neglected or if you have something really important to discuss, just send us another email.
i  n  f  o  (  a t  ) 0  x  9  0  .  s  e