To look at another players screen when comencing in gameplay, to benifit the cheating dink.
Most commonly used by men with small penis.
Side effects my include: increased hair groth on penis, facial deformity and loss of penis and/or penise(s).
WARNING
screenjacking is contageous and will spread quicly through your enviroment, if you come across a screenjacker IMEDIATLY close your eyes and masturbate for the best.
An Example is below.

while looking at one's computer, the surprise pop-up ad that appears independent of the user's actions. typically, this pop-up ad appears to block out the whole screen, and is difficult to close out.