Most internet users dislike them with a passion and web browsers have tried to banish them, but it seems that pop-up adverts may be popping up again.
Pop-up internet ads are disliked but are they making a comeback?
Web developers have fought hard to create technology enabling people to block pop-ups, adverts which appear at random and are difficult to remove.
A reported rise in pop-ups in recent weeks, however, has raised fears that such technology can be bypassed.
The recurring problem will have many web users pulling their hair out.
Winning the battle?
The industry has been starting to win the battle against pop-up ads in recent years after criticism it had not done enough to tackle the issue.
The development of web browsers such as Safari, Firefox and Mozilla containing software blocking ads was seen as a huge step forward.
Microsoft, whose Internet Explorer browser has 90% of the market, has also taken steps to clamp down on pop-ups.
Last August it launched a comprehensive security toolkit for its Windows XP operating system, including a blocking facility.
However, there are concerns that the technology might not be sufficient to see the back of pop-up ads once and for all.
"Pop-up ads have never gone away even though they are now less prevalent than they have ever been," says Mark Wood, sales manager for web analysts WebSide Story.
He says companies have found ways to "spoof" the technology.
They do this by sending messages using a different code - known as 'pop under' boxes because they open under the browser window - which cannot be detected.
"They con the browser into thinking it is not a pop-up and that it can display it. It is obviously a problem by the sounds of things."
Despite increased sightings of pop-ups, observers stress that blocking technology is largely effective and its use is now widespread.
In a 2004 survey, Forrester Research found that a third of US online households used ad blocking technology.
"Consumers are increasingly embracing a range of services and technologies to fend off advertisers' intrusions," said Forrester analyst Jim Nail.
"Their experiences to date have fuelled interest in blocking more ads on more media."