I have read that if your computer gets hacked you can't be really sure that you have a clean system even if you manage to stop the hacker and the best thing to do is to reinstall your OS. Do you agree with this?  What about different types of file including audio,video,pdf and executable files. If I move them to an external drive is it enough to scan them with an antivirus? If the antivirus says that it did not find any threats, can I trust it? Is it correct at least 99%?
What should I do if my Windows computer seems to be infected with a virus or malware?  What are the symptoms of an infection? What should I do after noticing an infection? What can I do to get rid of it? how to prevent from infection by malware?   This question comes up frequently, and the suggested solutions are usually the same. This community wiki is an attempt to serve as the definitive, most comprehensive answer possible. Feel free to add your contributions via edits.
Why on the first page Google says there are thousands of results but on the last page there are less than a hundred? .       The  has no sign of the user sharth The  also does not have any sign of related activity   I would like to know why the user's name is associated with the question. At least why their display name shows up as having modified the question timeline activity.  Possible reason that I can think of is that, .  Is this the reason?  Is there a way (for normal users), to look for such details, other than looking at the user activity and the question's revision history. Do photons truly exist in a physical sense or are they just a useful concept like $i = \sqrt{-1}$? Reading about photons I hear different explanations like "elementary particle", "probability cloud", "energy quanta" and so forth. Since probably no one has ever seen a photon (if "seen" it supposedly - and rather conveniently - ceases to exist) but many experiments seem to verify its properties (or are they maybe adjusted to fit the experiment). I thus can't help wondering if the "photon" is then just a physical/mathematical tool with inexplicable properties (like zero mass - but affected by gravity fields - and constant speed c in space) invented to explain some otherwise unexplainable phenomem and to supplement the elementary particles and their interactions. In short: Are they real or imaginary!  Does anybody know? Or maybe the answer is "blowing in the wind" because to most physicist it probably just does'nt matter as long as it works (as the alternative healers say). Sorry if I seem a little sarcastic here and there. Typo in First Posts queue If you go to the First Posts review queue, and if there's an answer in the queue and if you hover with your mouse over "No Action Needed", then you get a tooltip "this answers seems to be valid":  But it should be "this answer seems to be valid". Is it always better to use the whole dataset to train the final model? A common technique after training, validating and testing the Machine Learning model of preference is to use the complete dataset, including the testing subset, to train a final model to deploy it on, e.g. a product.      My question is: Is it always for the best to do so? What if the   performance actually deteriorates?   For example, let us assume a case where the model scores around 65% in classifying the testing subset. This could mean that either the model is trained insufficiently OR that the testing subset consists of outliers. In the latter case, training the final model with them would decrease its performance and you find out only after deploying it.   Re-phrasing my initial question:     If you had a one-time demonstration of a model, such as deploying it   on embedded electronics on-board an expensive rocket experiment, would you trust a   model that has been re-trained with the test subset in the final step without being   re-tested on its new performance? Trying to search for multiple file extensions in command line I am trying to find two extensions in command line but when i do it will only return one of the extensions. can you tell me what I am missing?   Here is my command;  [root]# find /etc -name "*.txt" -o -name "*.log" -type f -mtime +7 -exec echo {} \; Is Canonical Livepatch not supported on non-LTS release like Ubuntu 18.10? Last night I thought to check whether Canonical Livepatch service is working fine after upgrading to Ubuntu 18.10 from Ubuntu 18.04. I know it was meaningless since it was working fine in Ubuntu 18.04. But to my surprise when I ran   sudo canonical-livepatch status --verbose   I got the error:   2018/11/03 23:11:05 error executing status: Livepatchd error: The platform Ubuntu 18.10 is not supported. exiting.   I am now confused, is the problem only on my system? OR Is Canonical Livepatch service not supported on Ubuntu 18.10?  I would therefore like to request my fellow Ubuntu 18.10 users to do the check and if someone knows the reason/solution please reply to this thread. How can I get a history of running processes Make the search box return results from all StackOverflowian sites? Given an alphabet of size $n$, how many strings of length $c$ contain every single letter of the alphabet at least once?  I first attempted to use a recurrence relation to work it out:  $$ T(c) = \left\{ \begin{array}{cr} 0 &amp;\mbox{ if $c&lt;n$} \\ n! &amp;\mbox{ if $c = n$} \\ T(c-1) \cdot n \cdot c &amp;\mbox{ if $c &gt; n$} \end{array} \right. $$  As there's no strings that contain every letter if c &lt; n, and if c = n then it's just all permutations. When c > n you can take any string of size (c-1) that contains all letters (of which there are $T(c-1)$ to choose from), you choose which letter to add (of which there are $n$ choices) and there are $c$ different positions to put it. However, this gives out results that are larger than $n^c$ (the total number of strings), so it can't be right, and I realised it was because you could count some strings multiple times, as you can make them taking different inserting steps.   Then I thought about being simpler: you choose n positions in the string, put each letter of the alphabet in one of those positions, then let the rest of the string be anything:  $$ {c\choose{n}} \cdot n! \cdot n^{c-n} $$  But again this counts strings multiple times.  I've also considered using multinomial coefficients, but as we don't know how many times each letter appears in the string it seems unlikely they would be much help. I've also tried several other methods, some complicated and some simple, but none of them seem to work.  How would you go about working out a formula for this? I'm sure there's something simple that I'm missing. Does the universe have a center? When were the 'and' and 'or' alternative tokens introduced in C++? I've just read this  from Reddit.  They mention and and or being "Alternative Tokens" to &amp;&amp; and ||  I was really unaware of these until now. Of course, everybody knows about the , but and and or? Since when? Is this a recent addition to the standard?  I've just checked it with Visual C++ 2008 and it doesn't seem to recognize these as anything other than a syntax error. What's going on? Are the following two sentences correct?     I want you to go to sleep.   and     I want you going to sleep.   If they are both correct, what's the difference? How do I transfer a file to my server using PuTTY? Collection of short stories; in one a spy attempts to escape detection on Mars's moon by moving faster than the spaceship can scan Simple Past vs. Present Perfect: "was" vs. "has been" Possible Duplicate:          As a English non-native speaker it is difficult for me to understand when I must use present perfect or past simple because in my official language there isn't the present perfect tense. I know that present perfect is related to something that happened in the past but its result is important now. But for instance:        The message has been sent.   The message was sent.      Please help me point me out any examples/contexts where I should use 1. instead of 2. I know that new arXiv papers usually appear in Google Scholar within a few days or weeks. My question is: if someone submits a replacement of his/her arXiv paper, does the new version of the paper also appear in Google Scholar? "Above"/"below" before/after a noun I have seen sentences similar to the following:  (1) See the reference above. (2) See the reference below.  And,  (3) See the above reference.  But not,  (4) See the below reference.  Are all these forms acceptable? Which is/are preferred in formal writing? I'm trying to remember information about a series of three books I read in the early 1980's (first book could have been published in the 1970's). The book featured a character who was a scientific creation of some sort. It was (initially, I believe) an assassin, and had the ultimate getaway scheme; with effort, it could change its body, becoming about 10 years younger and switching sex. It changed 4 or 5 times in the first book, coming down from a senior citizen to someone in their teens or twenties; in the second and third books, it changed once per book (by the last book, it was a child or a young teenager).  The first book was title something like "The Morph..." where whatever the word was that started with "Morph" was this creature. No recollection of the author's name, or the titles of the other two books.  I think the cover of the first book was predominantly yellow, with black silhouettes representing the character at the four ages seen in the book, and a black title. And/or, the book might have been published by DAW (all their books at the time had yellow spines with black letters). Is there a way I can avoid imperial ships? Whenever I am traveling on foot, imperial ships will fly by and drop down troops for me to fight. In a normal situation, this is no big deal and I will fight or flee to continue with my travels.  However this will also occur when I am doing a quest that requires me to locate and pick up items. This is an inconvenience as I cannot pick up items while in combat and I have to kill them before I can continue.  Is there a way I can "hide" and allow the ships to by pass my location?