There is a "popup" type window, that suddenly appeared on my Windows 7 laptop one day. Its a rectangular window, with few lines of "random" sentences, that don't make any sense whatsoever. Like, "Some message", "Some text", "Subscribe now", "EVAL TEXTTTTTTT". There is an "x" button with the label "Hide this message", I clicked on it and it won't go away. Not very good with computers so please slow it down for me. I also did a full scan check, and it still didn't destroy it. So i don't know what to do, quite frankly.

If you run Task Manager and go to the Applications tab, select the line corresponding to the displayed text, right click and select Go to process. What is the executable? In the Processes tab you can do View -> Select columns, then choose Command Line. That will show the fully qualified path and file name of the executable.

Perform a system restore to a day or two before the problem started. If you don't know how:
Click Start and type: restore
Click on "backup and restore"
Click on "recover system settings or your computer"
Click on "open system restore"
Click next, then go through the list that shows up and choose a date that was BEFORE the problem was first noticed. Once you find a date, click it, then click NEXT.
On the next page, click finish. Then don't touch it until it's done doing the restoration. Don't worry, you won't lose any personal files. System restore only reverts drivers and applications.
Let us know how you make out. It definitely sounds like you've got a virus.

commented: Time traveler? Restoring the system only resets it to an original installed state - all data will normally be lost! -3

A virus is likely, albeit a badly written one. Run your A/V scanner on the system. If you don't have one, either install Microsoft's one, or ClamWin (free, open source), and scan your system.

EVAL base 64 file infector. There is a video showing a manual removal/php file-cleanup, and another site boasting of an automated tool, but Avast declares that to be a malignant site with a rampant php infector...

You might like to try two free anti unpleasant software detectors.
As you are using windows you can download from microsoft a program called microsoft security essentials and run that for free. there is also a similiar one called iobit Malware fighter and googling that will help you find the free version.!
Finally for a very careful cure for most items like this run regedit from the start menu to get your registry on the screen. BE CAREFULL.... first USE the file part of the regedit program make a back up of your registry.
Then using the find command (under edit or press F3) search through the whole of the registry for any or all the various text messages that you get and DELETE the key that contains that entry. You may have to insert a unobtrusive value but usually the delete should work.
When you have finishedf and do be very carefull.... if in doubt leave well alone! restart your machine using a full proper finishing and switch off power routine.
Whilst this method is long and fraught with some danger, done carefully it can be very effective for getting rid of annoying popups, as well as viral infections. (-in some cases the registry entry will tell you what actual exe file is that also may need deleting).
Take care and if all goes wrong you can go back into reg edit and reload the backup that you made (even in safe mode) to restore where you were before you tried to correct the registry.

Best of luck
M

Malwarebytes (free) should fix this. Let us know how you go on, please.

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